A Guest Blog by Stever Herr

PROLOGUE by Hector Medina (Editor)

As humanity moves along in its "progress", it is more and more clear that the only thing that is constant in the UNIVERSE, is: change.

The modern world has brought a number of inconveniences (like worldwide running Flu's), a number of disasters (like Global Warming), and a lot of veritable Tragedies (The continuous State of War since the beginning of the 19th Century).
BUT, it has also brought serious marvels; some of them, undoubtedly, double edged swords that can cut either way.
Among those marvels is the Internet and the level of communication that we can have now with people we have not ever met face to face. And, yet, the commonality of passions, the willingness to suspend (or lower) the "offense" level, and the usage of a "lingua franca" (English), allows us to work; share knowledge, ideas and experiences; and grow together with people that are hundreds of miles away, or thousands, it really doesn't matter.

And that enriches our life. Yes we can cuss the internet for the amount of garbage that we receive on the EMail everyday, but we also have to be grateful for the genuine and wonderful communication opportunities it affords us.

This FOUR PART SAGA is the result of one of those opportunities. A veritable "meeting of minds" that resulted in some fantastic experimentation and some solid science being made.

And so, without further ado, I yield the floor to the Steve Herr, the Gentleman from Pennsylvania, noting that it was a privilege and a pleasure to work with such a fine mind in these experiments.

​A 56TH Gone Awry
About 7 months ago I purchased a Diana 56TH in .177.  This was my first Diana with the sliding action design and I was anxious to give it a try.  After much reading and correspondence with Hector Medina, I tore into the rifle, going over everything from top to bottom.  The sled mechanism was polished up, T06 trigger disassembled, polished, relubed and set to a mere 8.2 oz pull.  The powerplant was replaced with an AGT 22mm skirtless design from Tony Leach, and the sled tension was tuned for best groups on target.
While I was very pleased with the results, I was seeing some fliers that concerned me.  It was shooting extremely well, don't get me wrong....but the fliers weren't going away.

After much work to try and resolve this issue, I turned my attention to the factory crown.  The factory crown had been machined at a slight angle, see attached picture.  When looking at the crown you could see that it was deeper and wider in the area of 1:00 O'Çlock to about 7:00 O'Çlock. You could also see that the grooves were blocked off along the edge in the area hi-lighted in yellow with only 5 of the 8 grooves being visible. 

​I finally decided to hand lap to see if I could improve on the crown, and help with the issue of occasional fliers. Using a brass hand lapping tool from Brownells, I went to work.  After the hand lapping, I was now able to see all 8 lands.  However, the crown was still angled.  If there is a lesson to be learned here, hand lapping will not correct a crown that is not square to the bore.  In fact, it may actually make the angle worse.
Here is the crown after Hand Lapping.

​After hand lapping I returned to the target to see if there were any improvements.  At 32 yards it was quite apparent that not only was the problem unresolved, but it had actually gotten worse with groups beginning to scatter.  As the title of this article indicates, this rifle was going HAYWIRE!!

After many hours of experimentation to try and resolve, I reached out to Hector to see if he knew of anyone who could re-crown a barrel square to the bore.  I was pleasantly surprised to find out that this was a service that he performs in most of his builds, and that he would be willing to look into my barrel in detail. 

We also discussed the heavy factory muzzle weight, and the tendency they may have in contributing to fliers.  He suggested some options for replacing the factory muzzle weight.  The options offered were a Harmonic Reducer or a more simple design called a Harmonic Tuner.  I said that I was open to his suggestions and would go with whatever he recommended.

A short time later my rifle was completely stripped down and the bare barreled action along with the barrel shroud was on it's way to Hector.

After evaluating the rifle, Hector began the process of re-crowning.  Here are a few pictures showing the step-by-step process.    Hector continued to machine the surface until the entire internal edge was the same depth and square with the bore.    If you look closely you can see how the crown was squared up nicely.  ​

On the final step, Hector added a taper around the outer edge, the end result being a nice target crown.

Hector's next step was to verify that the barrel would shoot.  In order to do this, Hector utilized one of his own powerplants, tuned to the desired level that I would be shooting the rifle (11.4 fpe), and using the same pellets that this rifle seems to prefer...JSB Exact 8.44 (4.53).  He also installed one of his stocks and a scope for the testing.
At 35 yards in a seated position (not benched), Hector confirmed that the rifle would offer up nice uniform groups rather than the scattered groups I had been seeing previously.

It was a HUGE relief to hear that Hector was able to save the barrel on my 56, and seeing the more uniform groups returning on target was extremely encouraging!
A job well done!!!
After the recrowning, Hector moved to the next part of the project, that being a suitable replacement for the heavy factory muzzle weight.  I will cover that in another write-up.

​
Steve

There has been a lot of interest in the 430L lately.
Probably as a result of the fantastic price that it's being offered at ($150 for a high quality gun is a great deal in anybody's book).
We have been working with the little rifle for some time now, but before we can go into "making it all it can be" we need to explain a little about how the GEOMETRY of a spring affects its characteristics.

To be quite frank, I owe a debt of gratitude to a young friend that plainly and to my face told me:
"You launched a bunch of information on materials when people do not really understand how springs even work"

So, yes, my fault. I should have posted this entry first and THEN the entry on Specialty steels now available for springs (which already have two reactions from spring/gun manufacturers). I do apologize for that and should have done things more in order.

So, Recapping:
Last entry about springs, we talked about the materials and how the different inclusions of metals as additives, or as alloying agents (not the same thing), change the behaviour of the material itself, it's capacity to store energy (as opposed to deforming permanently with it), and the spring's resistance to fatigue.

In this entry, we will explore a little about the science of "resistance of materials"  and, hopefully, we will help our kind readers understand the concepts and the relationships between single characteristics/variables that make or break (pun intended) a spring in an airgun. By the end of the entry, we hope that the readers will have a fairly good understanding of what "stress" and "strain" are, what geometrical aspects of a spring define those two quantities, and how the numerical values attained by those quantities relate to the "fit for purpose" quality of the material being used for an airgun spring.

Elastic/Inelastic.- The first thing we need to understand is that ALL materials are partly elastic and partly inelastic.
By elastic we mean that: IF subject to a force, and retained in place by some resisting mechanism (otherwise the object would simply move), THEN the material will deform in a proportional relation to the force applied.
By inelastic, we mean that the material, IF subject to a force and retained in place, will deform in a manner that is NOT proportional to the force applied.

Elastic limit / Yield Limit.- We have all seen relatively stiff and hard materials (like structural steel), bent beyond any recognizable shape, whether in a car crash, an explosion, or a building collapse due to some human error (the New Orleans Hard Rock Cafe Hotel being the most recent that comes to mind), but this tells us that even a metal that is DESIGNED to be stiff and resilient, turns from elastic to inelastic when the force becomes too much to bear. Materials Science aims to understand WHY and HOW, so that materials can be improved over time.

Stress and Strain.-
Stress is what we, airgunners, understand in HPA (High Pressure Air), as "Pressure". When applied to "solids" it cannot distribute evenly all across the material, as it does in gases or liquids, but it is the same concept: A FORCE (vector) applied over a surface, its units are pressure units.
Strain is the deformation of the material when subject to a stress (note that we now do not need to establish that there is retaining mechanism because the actual presence of an INTERNAL "pressure" in the material actually tells us that the material is being restricted and is accumulating that pressure inside the material components). It does not have units, as it is a proportion of whatever dimension the material had before being stressed to the dimension of the material when subjected to said stress.

Example: Let's think of a rubber band. Simple office/household/workshop/sports device. It can be the rubber bands obtained from old inner tubes you used when you were a kid to build your slingshot, or it can be the rubber band that holds the deeds, wills, contracts, and other important documents in your house fireproof safe.
We know that, if you apply a force to extend it, while retaining the other end, the band's LENGTH grows. We may also have noticed that the band's width and thickness were REDUCED by the extension of the length.
We surely will have noticed that if you pulled too hard on your slingshot, sometimes the subsequent shots came out "weak", or that if there are too many documents in the sheaf, then the rubber band seems to not hold them as well.
It means we have exceeded the elastic limit of the rubber band. That is, the point where stress and strain stop being proportional.
Using our new words, we can say that the stress induced in the rubber band by our pulling exceeded the allowable strain (yield point) for the rubber used in the band.
Savy slingshot builders will know from experience that there are many ways to build a better slingshot, but probably the easiest is to use surgical tubing instead of rubber bands made of cut inner tubes.
By improving on the material used, we built a better product.

Interesting so far, but, if you stop to think: ¿Can you compress a rubber band?
Hmmmm.- not really so, ¿how come we can compress steel springs, but not rubber bands?

Of course the answer lies in the geometry, but also in the way the molecules/atoms of materials stick to each other.

Some materials form crystals, some create amorphous structures. A Crystal is just a material where the molecules of the material are arranged in a geometric pattern, and therefore they resist pretty well any force that tries to tear them apart (operative word here is TEAR).
An amorphous material is a material where there is no geometric pattern, but still the molecules bind to each other by electromagnetic forces and therefore resist forces in a less "stiff' way, but they do resist deformations.

That sounds logical? Hope so, it still does not answer why we can compress steel springs, but not rubber bands.

Are there any examples of pure crystalline materials? Almost. Jewels are a good example, they are not perfect because even the most perfect diamond will have inclusions and flaws. It is THESE that the experienced cutter uses to split a large chunk into smaller pieces that can then be sold as the engagement ring stones that start most couples in the long road to family bliss.

IF the rough diamonds were perfect, there would be no way of cutting one in an orderly fashion and the huge gem would most likely explode if someone tried to cut it. It would have to be eroded/ground away little by little and a huge "rock" would be the result, like the British Crown Jewels.

Is there a perfectly amorphous material? Play Doh comes to mind. It does have SOME spring to it, but very little, so that little hands can create things out of it.

Between these two extremes, everything else in the world finds a place.

Now, ¿why steel?

We use steel because it is a fairly abundant mineral (Iron/Fe), therefore cheap. And we have been doing research and development on it for about 3,200 years.

HEY! Someone will say: We still do not know why we can compress steel springs and not rubber bands!

Yes, I know, we're getting to that, Patience and Perseverance, my young Padawan.

So, Iron, in its relatively wild state, is an amorphous material (Iron Oxide for the most part). and even when reduced in a kiln and rendered into ingots, the amount of carbon inclusions present as a result of the smelting process will make the "pig iron" fairly brittle. ¿Is it brittle because it is crystalline, or because there are lots of impurities and inclusions? Actually both.

PURE iron would be a crystal (actually there are two types of iron crystals, both cubes), albeit unstable ones (but that would be getting into Quantum Physics and that is beyond the scope of this entry), and so it would be brittle. It is also brittle because the casting process creates stresses along lines of non-homogeneity (impurities and inclusions), and because SOME forms of steel in the iron would actually act like a "wedge" in the material and make the stress fractures grow  rapidly and uncontrollably.
Assuming a very high degree of purity in the iron, then it would bend easily. Not much stronger, stiffer, nor resilient than the best Bronzes.

So, we refine and change the pig iron into steel by including and diffusing the carbon content (reduction process of the oxide, and then purposely oxidizing the excess carbon by blowing air into the molten metal), and then increase the content of other metals, and non-metals, to increase other characteristics (hardness; stiffness; resistance to fatigue, to high or low temperatures, to oxidation, etc); from Molybdenum and Vanadium, to Copper, Silicon, Manganese, Chromium, Nickel, and Cobalt.

Now, the elements above mentioned, whether added as alloying agents, or as additives, diffuse themselves into the crystalline lattices that iron forms. And when temperature is changed dramatically (quickly) either in a quenching, tempering, drawing or other thermal process, then further compounds form: Carbides and Silicates being the prevalent ones.  More important than the compounds is how the crystalline structure in the steel changes with heat treatments.

When we said that Iron creates two types of crystals, we were referring to a Body-Centered Cube (2 Iron atoms) that is called Ferrite, and Face-Centered Cube (4 Iron atoms), called Austenite.
When the Austenite cools down abruptly, it shears the cubes into two tetrahedrons, where the carbon is diffused into a much more compact space, and therefore the crystal itself exhibits very high "strength". Problem is that it also become brittle. These tetrahedrons structures are called Martensites and they are the ones most responsible for the hardness in steel.
Since the crystalline structure change is forced by thermal processes, it is mostly, and controllably, reversible. So, for every quenching, there must be a tempering and a drawing, in order to create a material that is "balanced" between hardness, stiffness and resistance to breakage.

Now that we have explained how the physical properties of steel change due to the change in the crystalline structures, we can say it:

We CANNOT destroy any material by "pure compression" . We can compress materials but compression by itself does not induce neither stress nor strain.

If you remember, when we stretched the rubber band, we observed the thickness and the width of the band to decrease. THIS is what WE call "compression", but in reality is the RESULT of a stretching.
The PROPORTION between the elongation in the direction of the stress that is being applied and the contraction in the perpendicular direction is the Poisson Ratio for that material.

In the same fashion, if we were to have a perfect cube of steel that we put it in a press and then apply force on it, it will fail not because we are compressing the material, but because the material that we are compressing is placing a STRETCHING force sideways into the surrounding, unsupported, material, and that is what tears the material apart (¿remember I told you that the operative word was TEAR?).
​
If I am not making too much sense, consider the same case, but in a hydraulic environment, where we apply a force to the fluid, and the fluid itself applies evenly and in all directions, a pressure to the steel cube.
¿Do you think it will fail?
.
.
.
Nope!

Let's conduct a "thought experiment":
Think of a material as a collection of "leaves", formally called lattices, and then let's think about how important is the directional connection of the internal structures of the material.
Imagine a sheaf of paper. While it is packed and in the wrapper, it can be incredibly strong and behave almost a like a solid brick.  You can stand it upright and you can stack a bunch of them one on top of the other.
BUT, if we remove the wrapper and try to stand a single one on its own, it will collapse.
While on the wrapper, we cannot bend a whole ream, but out of the wrapper, the whole ream can be bent and fanned, and "aired", as we used to do with the feedstock of old copying machines.

IF we apply enough force to a wrapped ream of paper, it will BREAK the wrapper, if we apply a little force, and then place it on a table it will return to is prismatic shape out of its own weight.
In one case we have exceeded the yield strength of the material, in the other we have not.

Important here is to stress that, when out of the wrapper, if we bend the ream one way, there will be one end that becomes "longer", if we bend it the other way, then it's the other end the one that becomes "longer".
In the middle, there will be one sheet that keeps its apparent length, and we will call that the "Neutral Fiber"

So, back to steel airgun springs: ¿What on earth are we doing when we compress the spring?

Savy airgunners and specially those tinkerers that turn their own spring guides know that springs will increase in Outside Diameter (D) when compressed.
If you think about it, a length of metal can only increase its length if it is being STRETCHED. So, when we compress a steel spring, in reality we are stretching each and every coil.
This stretching is what induces the stress and the strain, and it is the reason why we must pay special attention to the SURFACE of the spring. Any imperfection or point of stress concentration will start a micro-fracture that, in the end, will break the spring.
Reason why good quality springs are shot peened and / or covered with some material that prevents the formation of micro-cracks.
Usually, when we receive a spring from a manufacturer, it is longer than expected, unless we specify that we want our springs to  be shipped "set". In this case, the spring manufacturer will compress the spring to solid and then ship it to us. By compressing to solid, the yield / elastic limit is reached and the spring is reduced to the shortest possible length. No further compression cycles can exceed the yield limit of the new conditions (length and diameter), and therefore all further usage will happen within the elastic limit of the material in question.

Can we make springs out of other materials? Yes, and we do. Beryllium bronze is used in explosion proof applications, copper is used in some other -mainly electrical- applications, even aluminum can be used but it's very limited; hopefully, once we master the creation of crystalline aluminum ("Transparent Aluminum" of Start-Trek fame), we will have a fantastic material, specially for scope building. That, though, is several years into the future.

One last thought experiment: If you drop a steel ball bearing into an anvil, it will re-bound. But, it will not rebound to the same height it was dropped from. Even in vacuum.
And if we measured the temperature of the steel ball, we would see that after many re-bounds the temperature has gone up slightly. ¿What is happening?
What is happening is that even the hardest of steels that can absorb huge forces and not yield, still cannot return 100% of the received energy.
SOME energy is lost in the INTERNAL FRICTION of lattices and molecules that bend and suffer recoverable internal displacements.
The SUM of all these INTERNAL energy losses is called Hysteresis

Now, putting it all together:
A material can receive a stress, accumulate it as a strain, AND RETURN IT as a force, only when the elastic yield limit has not been reached.
It will not return ALL the energy, some portion of it is inevitably lost to hysteresis.
The Elastic Yield Limit will be determined by the structure of the material as much as by the chemical and crystalline arrangement that is controlled by post material manufacture heat treatments.

So, now that we understand how springs work; how materials work, and fail; and how we need to look at the limits of the material to select a "fit for purpose" material for our springs, we can go into the GEOMETRY.

Let's dive off the deep end and go directly into an equation:

Frightening, ¿Isn't it?

And yet, this equation says nothing more scientific than if I would assert: "The moon is a huge, spherical, rock that goes around the earth in ever increasing ellipses governed by Newtonian physics"

Both, the equation and my assessment, are true and consistent with the human experience of thousands of years. Both give humans a good frame of reference to study the object of interest, whether it is the moon, or the coil spring. Both can yield good insights into what the effects of changes can be. 
And yet there is a degree of empiricism into both, they are not "pure science".

The reason is simple:  since the formation of the moon from the proto-earth to the present, there have been many phenomena that have taken place that we can neither prove, nor disprove. So we can only establish theories of HOW the moon came to be, WHY it is going away, and WHAT happened in the past that cannot happen in the future because the distance to the moon is only increasing.

In the same way, the complication of a coiled wire that changes apparent cross-section with each millimeter  of compression, that is subject to microscopic heterogeneity and that can have vastly different characteristics, while at the same time having vastly different histories, is very hard to pin-point.
BUT
The experience of the last 162 years (since the machine to economically make coil springs was invented), has shown that it is "Close enough".

And, so, let's take element by element in the equation into analysis and consideration:

"k"

k is the constant of the spring. In other words, how much force it can store for a given length of compression. You can think of it as lbs(force)/in, or Newtons/m, or kgs/m, or oz/in, or . . .
In the end, you will have a rifle with a power stroke of length "X" and you will want a spring that can develop "Y" force, so that the piston can be accelerated and pushed into the compression chamber that will make the air inside go through the transfer port and push in its turn the pellet out of the barrel, ¿no?

So, given an ARCHITECTURE of a gun (power stroke, bore, swept volume, piston's mass, and transfer port length) we can estimate how much force we will need, and therefore, what characteristics of the spring we need to achieve.

OR, assuming an average efficiency of the basic airgun architecture, we can also start from desired energy yield at the muzzle and go back all the way to the force required and therefore the "k" we need to achieve within the constraints of both the gun and the spring material.

So, let's simplify, clarify, and amplify (SC&A):
"k" just means how strong the spring will be, given a length of compression, it comes from Hooke's  Law that states that  'F=kX' where F stands in for Force, k is itself, and X is the power stroke.

"G" 

Is the "Shear Modulus". It means how rigid a material is, how much stress is required  to create the necessary  amount of strain that will tear the material apart.

It CAN be calculated using the Elasticity/Young's Modulus (the tangent of the angle of the line that describes the stress-strain behaviour of a material in the linear -elastic- zone; also called the slope of the curve in this first section -before the yield point-) and the Poisson Ratio (the relation between a stress applied in a direction with the strain created in a perpendicular direction).

Now, BOTH the elastic modulus and the yield point, as well as the Poisson ratio are determined experimentally for specific materials, again, this is empiricism. So, there are tables that tell us what are TYPICAL Shear Modulus values for different kinds of steels and other materials just for the sake of comparison:

As you can see, the range of "G" for economically viable materials is pretty narrow: between 76 (GPa) for "Nickel Steel" (basically stainless), and 79 for "Structural Steel".

I am including other materials just for the sake of comparison, and if we go to serious spring makers' websites, some of them list the characteristics of the materials they use.
Still, a pretty much uniform value for G is around 79.3 GPa for ALL steels that are of viable use, whether they are labelled as "valve" or "specialty" steels.

​So, SC&A: G is, for all intents and purposes, an empirically derived value that for airgun use should be taken as the constant 79.3 GPa/11.5 Million PSI

"d", "D", and "na".-

"d"  Is the diameter of the wire used. Using a fairly standard diagram:

"D" is the mean diameter of the spring, or the diameter between the neutral fibers of the steel used in making the spring, which just means that we need to subtract one wire diameter from the Outer Diameter.
A little like calculating a center to center group size: You measure the two farthest edges of the two extreme shots and deduct a caliber. Same process, same principle, same arithmetic.

"na"  is the number of active coils, which for most purposes (except Vortex's PG-3), would mean the number of coils that are ACTIVE, therefore the two end coils do NOT count.

SO;  By now we have almost everything we need to start playing with the numbers and understanding how one variable affects the possible outcomes.

As usual, since the advent of computers and the internet, there are online calculators that do the number crunching, this is one of them:
https://www.acxesspring.com/spring-calculator.html
and it is fairly easy to use.

Let's try an example:

We take the 640 T spring from ARH's website:
https://www.airrifleheadquarters.com/catalog/item/251488/8128905.htm

Just because it is new and it provides an interesting contrast with most other springs offered. It is a WIDE spring : 0.640" ID, with a relatively thin wire: 0.120", 35 coils and an OAL of 13.25" (unset).

The 0.640" ID would mean a 0.880" OD and a "D" of 0.760" or 19.3 mm's

So, what would the calculator predict?

And so, we have the force that the spring can store: 20.564 #/in with those design parameters.

But, what would happen if we increase the Wire diameter (for the purpose of this numerical simulation, we will change ONE thing at a time.

Let's go to 0.130" wire:

We've gone from a k of 20.564 to a k of 29.47, this is a HUGE increment for a mere 0.010" in diameter of the wire.
But then, remember the equation? In the equation, the d is raised to the 4th power, so a 9% increase in wire diameter would imply over 40% increase in k.

What would happen if we had REDUCED the mean diameter of the spring?

Let's go back to our 0.120" wire and reduce the OD to 0.774" that would imply a D of 0.654:

Now we have a k of 32.272 #/in.
Why that value? because that value gives an ID of 0.534" that is a tight fit into the OEM DIANA spring guides.
What would the equation have predicted?
A reduction of 14% gets raised to the power of 3 in the divisor, so the net effect is an increase of 57%
For a base case of 20.564, a raise of 57% would mean 32.27 #/in, so we now have a feel of how changing one aspect affect the outcome.

The last variable we can play with is the number of active coils, but that is an inverse relation, so it is not too complicated to imagine what effect reducing, or increasing the number of active coils will have in the result.

Ideally, we should choose the biggest OD that will yield the power we are looking for.
We can increase the d, within limits, and every gun will achieve a "plateau" where more force will not increase muzzle energy because the swept volume has been completely used.

The biggest possible OD will yield the least stress in the spring, therefore, this will guarantee the longest and most stable life possible.

For most calculations, the springs we use in airguns are doomed to failure because calculations cannot take into account the effect of a guided spring (fore and aft). SOME calculators do, but you need to pay for them and it is not in the intent of this blog to make you pay for information.

Most spring makers would balk at the duty cycle we submit our springs to. But then they are concerned mostly with industrial applications where millions of operations are desired before you need to shut down the plant for maintenance. Maintenance, for some of us, is part of the hobby.

In the next blog entry, we will deal with what can be done to the DIANA 430L, short of changing the cocking lever arrangement, because that will be looked into in another blog entry that will deal with efficiency of powerplants.

Hope you have enjoyed this trip into the rarefied world of the airgun designer.

I apologize for the length of the entry and thank you all for staying with the thread of ideas. It is a complicated aspect to explain and I hope I have not confused everyone even more.

;-)

Keep well, shoot straight, and if I don't get the time to write the entry for the 430L before the holidays come tumbling down on us, like the walls of Jericho, I wish you all, the best of peaceful, contented, filled with family and friends, holidays!






​HM

If this sounds like the header of cooking thingy, you're right, LOL!

I am seldom enthused by the modern pellet trap offerings.

"Silent traps" that rely on duct seal to reduce the noise are a pain to clean the pellets from and, in the end, you are left with a lump of contaminated material that is impossible to recycle, or extract the lead from. Little shards/shrapnel are extremely difficult to find/remove.

Cardboard boxes filled with rubber mulch work real well, until you need to clean them/extract the lead. Dumping everything in water works so-so, as it is a long and messy process and you end up with a bunch of wet mulch that takes a few days to dry. If you put it into new cardboard boxes, these get wet and loose all resistance.
Also the raffia web that is most useful to hold the mulch in while allowing the pellets to enter but not allowing them to go out is not easy to get.

I've also tried the "curtain" type of traps, where hanging pieces of cloth are supposed to slow down the pellets enough so that the rear steel plate backer can stop them. Useless by the 100th round, curtains were replaced with genuine sown Kevlar cloth, in itself a pain to do because cutting and sewing Kevlar is not precisely easy. And it was still a mess.

Normal, "assemble yourself" pellet traps rated for 0.22" RF cal. have the great defect that they have a junction where the rear of the slanted plate and the horizontal plate meet, and lead shards/dust escape through there.. NOT ideal.

Those that are welded are, by far, the best option, but they are not truly portable, weighing in excess of 20#

​So, when I saw this pellet trap at a Cabela's store:

I was almost going to just jump over it, when something struck me: It looks VERY similar to the old "Cabañas" pellet traps that I used to use in México
Picked the box up . . . . Hmmm, light enough
How does it go together? Pretty easy.
Hmmm, well there is a well to catch the spent pellets!
Rating? apparently 0.177" pellets, but when you read the small print, it is 0.177" lead pellets at under 800 fps from a distance of at least 10 yards.
Still, the design was good, it had "Possibilities".

When I reached home, I took some measurements and contacted the good people at Online Metals to see if they would be so kind as to cut steel plate to measure.
They agreed, and so I ordered four 0.19" x 7" x 7 1/2"  ANSI 4130 annealed steel plates (yes I will be constructing a few more later) and they came out at $25 ea.
Great service and great prices. Online Metals recently became part of the Thyssen-Krupp corporation so, you could say that they know a thing or two about steels.  ;-)

In 3 days I had the plates and then "cooking" started.

Then the trap backplate was marked, punched, drilled and deburred:

Short Allen-headed bolts were inserted into the trap's backplate:

1/4" rubber grommets were used to space the plate and deaden the sound:

The resulting "air sandwich" can be seen here:

Then assembly took place as normal.

You can see that the short (10 mm's)  Allen bolts do not protrude from the plate's surface.

And if you do not want to use the swingers, you can use a standard target:

Do take the precaution to put a cardboard and a "foamy" backer behind the paper target. Between the two they will stop any ricochet and all dust and shards will remain behind the backers.

A suitably sized cork stopper can be used to plug both "exit" holes:

Methinks I'll  have to open a couple of good wines, LOL!

Anyway, it took about 10 mins to order the plates from Online Metals. And ordering the "Air Strike" pellet trap can be done directly from Do-All Outdoors or from a number of online retailers at between $17 and $20 per unit. Personally I would not spend more than 5 mins to save $3, but to each his own. Shipping may or may not add to your cost.

Marking, drilling and tapping, and then assembling everything took about 20 minutes.

3/16" plate will stop almost every airgun pellet, just do not use "penetrator" pellets, with steel balls, or bronze points, or other gadgets like that, and you will be fine.

While not completely silent, it is much easier to clean and to retrieve the lead from. Babies can sleep at two doors' distance and not be bothered by the noise.

Do NOT use for ANYTHING OTHER THAN AIRGUNS AT UP TO 35 FT-LBS ME WITH LEAD PELLETS

DO NOT EXCEED 35 FT-LBS MUZZLE ENERGY

ALWAYS WEAR SAFETY GOGGLES  WHEN SHOOTING AT LESS THAN 30 YARDS

I hope you enjoy this short project. I did!

Keep well and shoot straight!







​HM

For some time now, I've been wanting to post this entry, but had been unable to find the time.
Courtesy of our friends at Aer Lingus, that delayed my departure from Washington (Dulles) and made me loose my connection to Birmingham (and the World's FT Matches), I've had to sit in the airport then attempt a boarding, only to be denied boarding on account of my "firearm".
You see, there are planes in the Aer Lingus fleet where you can access the hold, so in those planes, "firearms" cannot travel.
It doesn't matter that it is a single shot, pellet rifle, disassembled, and unloaded (obviously, who in their right mind would carry a cocked springer without a stock and with an exposed trigger?!)
The computer terminal says it cannot travel and the employees cannot exercise neither judgement, nor criterion, they are not allowed to think.

We'll limit ourselves to the metal (steel) coiled spring for this entry. If there is enough interest, we can talk a little about gas springs, but the metal spring is complex enough to warrant a complete entry on its own.
Let's start with some clarification of concepts:

A steel spring is a series of coils. You might say that is obvious, but the truth is that what is not obvious is that each coil behaves more or less independently and in those things where they act together are those factors that affect the interlinkage of the coils and have the most effect in the long term life of the spring.

Like a train, if a spring is not properly "loaded" it will get de-railed.
Experienced railroaders know that if you put the light cars in the middle, and the heavy ones in front and in back the train "stretches" and cannot follow the tracks (like "Tootle").
So, trains are "loaded" in certain order and then locomotives are inserted at strategic points in very long trains (in excess of 100 cars).
It is not uncommon in the US to see long haul cargo trains with up to 16 locomotives distributed along the beginning, the end, and both(1st and 2nd) thirds of over 170 cars.

An airgun mainspring is not that different.
Its relation of Overall length (OAL) to Outside Diameter (OD) renders them very "slender", and so, prone to "derailment" (kinking), stretching and knocking (twang), and even bumping (buzzing or vibrating).

So, how could we build a better spring?

​SOME improvements could come from the science of materials.

In the automotive industry the effect of different alloys, heat treatment, methods of heat treatment, surface finishes and even coatings has been studied in depth.

Those of you that are old enough will remember that valve springs would hardly last 10-15,000 miles without loosing some of its "oomph", this required constant "tuning" of the engine. Usually, every 3-5,000 miles, and then change of springs.
Modern valve springs will last well over 100,000 miles.  Even "racing" springs can now last at least a season (not an interesting aspect in high budget racing, like F1, but interesting in other forms).
Up until 50 years ago, High Carbon steel spring as produced by the US or Swedish firms was the top material. A concerted effort on the part of Japanese car makers brought a full range of innovations: Chromium was added, then Silicon, then heat treatment prior to winding, then Vanadium was added to the wire (not as an alloy), lastly Cobalt; and very serious studies have been conducted about what is what TRULY defines the fatigue and temperature resistance of springs, to this date, most (by volume) truly high quality spring steel is produced in Japan.

Of course, given the vertical integration of the Japanese economy where the same "group" is composed of companies ranging from mining conglomerates to car making (Mitsubishi is a good example), or where the close alliances between industry, banking and commerce create de-facto groups (Sumitomo), it is not complicated to setup an institute to research these things.

Luckily, they are generally open with those things that are at least 5-7 years old, and we can take a peek into what it is the current, published, state of the art.

So, let's compare how successive generations of valve spring steel compare to "piano wire" or "conventional steel":

Do note that this table is courtesy of Sumitomo Electric, so the names  of the steel are "commercial":

This is how the Japanese standards call and classify the steels used:

Do note that, by now, the Carbon (C), Manganese (Mn), Nickel (Ni), Chromium (Cr), and Vanadium (V), have reached pretty uniform compositions, and the difference between one "normal" grade (SOTHN) and the "super" grade (SWOHS) is a small further addition of Silicon (Si) 

And this is where Sumitomo is currently, adding Cobalt (Co):

Now, if you are wondering why the complication in adding more and more materials to the alloy, and also to the metal itself, it is mainly because the current, complete process of spring fabrication is a lot more complicated than just "winding":

Those of you that have some experience with materials and heat treatment will wonder why the quenching shows a higher temperature than the drawing or the tempering, and this is something that is peculiar to these very complex steels:

Pulling the wire through dies creates some work hardening as it is "drawn", but then this hardening needs to be quenched in molten baths (either lead or salt composites) at a higher temperature than that of the drawing.
Steel at this point would have little hardness and little tenacity/toughness, so it needs tempering.
After tempering, then the spring is wound or coiled.
But this tempering process, even if it is conducted at relatively low temperature, requires some annealing in order to make the spring less fragile.
Then the surface is treated with Nitrides in order to create a "case" that exhibits superior resistance to the starting of cracks and fissures which are the weak spots where the spring breaks, while still retaining a "core" with tenacity and toughness.
But while niitriding creates the chemical aspects conducive  to surface hardness, it also stresses the surface itself. So these stresses need to be relieved and the most economical way to relieve them is to "shot-peen" the spring (some manufacturers use small bits of wire to shot peen, not actual spherical shot).
Finally, the spring is subject to a certain portion of maximum allowable stress and "aged" by the strain this stress creates (what we would call "setting", though we set the springs by compressing the FIRST time to fully solid condition).

There are techniques to strain-age airgun springs, but not all airguns are suitable for them.

After all these processes, the resultant spring is capable of MILLIONS of operations within the design parameters, and here we note that NO AUTOMOTIVE spring reaches the compression ratio of airgun mainsprings.

Would an airgun spring manufacturer be able to buy these super-special steels?

Maybe, I really do not know. My calls for information went somewhat unheeded as to what material each manufacturer uses, so I cannot tell you who uses what and what processes are applied to our airgun springs.
I am sure that they all do the best they can within the constraints of the costs they can face. And this is an important consideration.
An OEM spring costs between $0.50 and $4, an aftermarket spring costs about $10, some VERY special aftermarket springs can cost up to $25, most of them are sold for between 2 and 3 times the cost, not all of them are truly worth the price the consumer pays but, when you consider that a gas spring, in industrial assembly quantities can cost between $5 and $25, it is clear that extremely advanced steel springs will never make it to the OEM piston gun.

We said in the beginning that a spring is a series of coils that act more or less independently from each other, and that is a good way to start to understand springs.
The first coil supports and pushes the second that in turn does the same with the third, etc. BUT if we think about this closely, we will understand that the first coil is pushing ALL the next coils, and that in the other extreme, the last coil is pushing the piston itself. 
Yes it receives the support and push from all the previous coils, but this difference make the "distribution of labor" different for each coil depending on WHERE that coil is in the spring.
This concept also clarifies that the WEIGHT each coil is pushing, depends on the position in the spring.
And lastly, this concept also helps us understand that once the whole length of the compression chamber has been run by the piston, and the piston itself suffers the pushback from the pellet's inertia/resistance and high pressure thereby developed, a whole mayhem of disorderly conduct ensues. Some coils go back while others go forward, and some stay more or less stationary. These "travelling waves" of steel actually make the spring perform several compressions and decompressions for every shot cycle.

The most common way to solve that is to use a tight fitting guide.
A tight fitting guide will provide some coils with enough friction to dampen their movement.
And so, we eliminate the twang and the buzz.
We also reduce the double and triple duty cycle that some coils perform.
But, as much as we would like to reduce completely this aspect, we cannot. We cannot introduce so much friction that the extra movement of the coils is completely arrested. We would not get the speed we need to drive the pellet.
So, we need to accept that as long as we use a coiled steel spring, we will need a tight guide, or accept the twang and the buzz.

The natural question here is: Why don't manufacturers use a tight guide from the start?
Answer lies in the cost, of course.
And the REAL answer is that to make the springs, the steel needs to be coiled (remember the 4th step in the manufacturing process?). 
How do we do that?
Some of you may answer that you take a mandrel, and coil the spring around the mandrel. 
Well, that was true in the old days.
Fairly elaborate mandrels were turned to set the "pitch" of the spring, and the diameters had to be not only calculated, but then rectified by actually making a number of springs.
Because, depending on the force you use to restrain the wire from winding freely, the spring will always be fatter than the mandrel; more force, less difference between mandrel's outside diameter and spring's inside diameter.

Nowadays, springs are wound using mandrel-less machines that simply start bending the wire along an adjustable curve and the spring wire is "pushed" into form, not stretched.

This means that you are not limited by the length of your mandrel. You can make REALLY long springs. And you can also adjust the dimensions to a fine degree: Inside Diameter (ID), Outside Diameter (OD), Pitch (P).
​
Some aspects that are seldom questioned are:  What is the INTERNAL geometry of the spring, and why, where and how does the spring accumulated energy?

To understand that we need to look into what is the "Neutral Fiber", "Neutral plane", or "Neutral Axis"

INTRODUCTION.-
One of the privileges, and pleasures, of being a custom airgunsmith and, partly, a sort of "Ambassador" for a well known brand (DIANA), is that I get to meet extremely interesting persons.
In particular, I have found airgunners to be a special breed of shooters and hunters.
Most of us are VERY ETHICAL in our hunting practices, and also extremely sportspersonlike.
Not that we can be characterized as "Adults",  LOL! but we are truly mature and rational "human beans" (yes, I do joke now and then).
For the most part.
Yes there are exceptions, but they are few and far between.

I met Matt Coulter when he reported in a well known forum (GTA) that his DIANA 48 would not cock and, finally, the cause was traced to the stem coming completely separated from the body of the piston. That, obviously, was a "Red Alert"; and with Matt's help, we were able to trace the lot and date where that piston was produced and steps were taken, and are still being taken, to improve on a method that is about 80 years old and that was useful when materials and precision machining capabilities were not what they are today.

Matt has an excellent background on Photography and Technical Writing, so it was almost natural for me to invite him to write, not about that piston, UMAREX stood honourably up to the plate and that situation was resolved, but on a specific interest of his, which was shooting with light-weight guns and, in particular, iron sights.

We've been working at this over the last 8 months, and there have been some of the normal (to spring-guns) disruptions and "events". All in all, Matt handled them all with aplomb and the resulting article is full of useful information that, for sure, will help those airgunners that are interested in good marksmanship, but not at the cost of adding a 2 lb optical "brick" atop their airguns.

So, without further ado, here are Matt's experiences and findings, hope you all enjoy the hard work presented here as much as I did.

OK, I will admit that I’m guilty of having a “Turn it up to 11!” mentality when it comes to rifle scopes and their magnification. Having studied photography and being a former photojournalist, I have always enjoyed and appreciated anything with a lens.  But, as “luck” would have it, my .22 caliber Diana model 48 ate my scope and fortunately, an opportunity to try a very different scope was presented to me and I jumped at the opportunity!    
 
Late last year I shared this scope-busting experience in an online post titled “Open sight fun w/D48” on the Gateway to Airguns forum.  Following this post came an offer to evaluate a diminutive, low-power scope.  To be quite blunt, I would have been quick to overlook this little scope when researching options for a new scope.  Outside of this offer to check it out, this specific model scope would not have been on my radar.  

And I’ll just come out and say it... on paper it’s really hard to get excited about a 3x32 scope.  But hold on a minute -  I’m really glad that I’ve been able to shoot with this glass.  There’s a TON that can be learned from a low-power scope.

Oh, by the way, I should also mention this is actually a crossbow scope.  Yes, a crossbow scope.   Specifically the Sightmark Core SX 3x32 Crossbow Scope. (Note by the Editor.- This scope is now discontinued and has been replaced by the 1.5-4.5X32 scope that presents the same facilities and more versatility)

Below are five revelations from shooting with the Core SX scope:
 
1.    Weight matters
Eight ounces may not sound like much, but when this mass is perched up on top of your rifle in rings, that extra half-pound difference can definitely be felt. The Core SX scope weighs in at 14 ounces and that’s a nice savings that can be felt over the 22 ounces of the other scopes I’ve used.

This 9-inch long scope works particularly well with the shorter length-of-pull on the Diana 48.  Would this smaller scope work on every gun?  Nope.  Using the Core SX scope on some rifles (without offset or cantilever mounts) simply would not be feasible.  My Kral PCP, with its very long (15-inch) length-of-pull, is  barely usable with my 3-12x44 compact scope.   For reference, here is how the Sightmark compares in length with a couple other of scopes:
Sightmark Core SX = 8.9 inches long
3-12x44 compact = 11.2 inches long
4-16x40 = 14.6 inches long

3.    KISS and relax
“Keep It Simple, Stupid” or KISS is a laudable credo to follow.  It is also one that pretty much defines the Core SX.  Its magnification is fixed at 3-power and its parallax set for 30 yards.  It does have an adjustable diopter (3 to -3), of course it has windage and elevation adjustments (.5 MOA), and an illuminated reticle.  The reticle markings are finely etched (not fat wires) and are quite crisp. The crosshairs and four holdover points below it are very easy to read and are specifically configured for crossbow usage.  These holdover points and are calibrated to 20, 30, 40, 50, and 60 yards with a crossbow shooting at 320 fps.
Spoiler alert - you may not need very many of the hold-over points with your typical airgun at 3x power  :-) ​

During my first weekend of informal testing I shot the Diana 48 off a monopod at distances that ranged from 10 yards to nearly 60 yards using JSB 15.9 grain pellets.  Here in Central New York it’s winter and temperatures during this testing were just above 20f.  The scope’s image at my zeroing distance of 10 yards was soft but usable.  The actual zeroing of the scope was uneventful.  Five shots downrange and I was hitting my bullseye.  Aside from my initial zeroing and then an elevation adjustment for a further distance, I did not do ANY further fiddling with the scope.  
The bulk of my shooting at 25 yards.  I can truly say that I was all smiles shooting at this distance with the Core SX.  While seeing how this scope and my rifle got along, it was not long before individual shots became groups.   Then those groups became defined enough to see through - even with a 3x scope at 75 feet!  ​

At this point I realized just how relaxed I was while shooting.  This became even more apparent when switching from the Diana 48 with the 3x Sightmark scope to my Kral PCP with a 4-16 scope.  One would presume that greater magnification would translate into better accuracy.  Well, my experience was a bit different.  I would consider accuracy between the Diana 48 springer and Kral PCP quite comparable at this distance.  What WAS significantly different was the additional energy and “focus” that was required to keep the crosshairs on target when shooting the Kral with the higher-powered scope.  I found that some of the fundamentals of shooting - natural breathing, relaxed muscles, and generally being in the “zone” - just came more naturally with the lower powered scope.  ​

With the winter cold beginning to reach my bones and my fingers getting numb, I figured it would be time for my final “Hail Mary” shots at a longer distance.  I set my target at roughly 58 yards and guessed the holdover might be the second mark below the crosshairs.  Fire the shot and listen… No telltale smack of the pellet punching its hole in the target.  Hmmm… This would be my 1st lesson on holdover with a 3x scope.  I was simply shooting too high.  A little bit of holdover at this distance was all that was needed.  A lower point of aim resulted in that satisfying smack of the pellet hitting the target.  No, I didn’t have a chance of seeing the .22 inch holes on my 60-yards target, but what is missing in magnification is made up for by a wonderfully bright and clear image.  Ultimately, I was quite pleased with not only hitting the target with a minor adjustment, but when I walked around the frozen pond that I was shooting over, I was actually pretty pleased with the resulting groups!

4.    Is seeing the barrel a bad thing?
The first view that I took through the scope after mounting it was an interesting combination of amazement and disappointment.  I was amazed at the brightness and sharpness of the image, but I was feeling deflated by the fact that the scope’s low-magnification allowed the barrel to be clearly visible in the bottom of the scope’s sight picture.  This dark blob at the bottom of the sight-picture slowly became something new and rather unexpected.  Seeing the barrel can actually be a HUGE advantage!    ​

5.    The incredible disappearing scope
No, I’m not talking about hocus-pocus here, but saying that the scope “disappeared” really was the best way to describe how it seems shooting with this scope.  I’m sure this effect is just a combination of the scope’s  low-magnification and large exit pupil, but more than any scope that I have used, this one allows me to see and visually engage both what is inside the scope’s field-of-view along with what is within my peripheral vision.   I found my brain really was able to blend the two seamlessly. ​

Trajectory Testing

The week following my initial scope testing brought weather that cooperated well enough to continue testing with the Sightmark crossbow scope. Even though the weather in Central New York is typical for mid-winter - cold with temperatures hovering around 20f - the wind was manageable, so testing was a go!  

I’m fortunate enough to live in a location where I’m able to shoot to distances just over 60 yards in my backyard which I would consider a reasonable upper limit for target shooting with a 3x scope.  Most importantly, this time of year, I was able to do this from inside a nice shed to be out of the elements.   ​

Initial scope calibration and trajectory testing began at 23-yards.  One of the first evaluations I wanted to run testing how changes to the point-of-aim (by using the hold-over points or “subtensions” on this 3-power scope) would  translate into changes in the point of impact.  ​

​As we can see, the results were quite uniform and  as expected we can see greater changes in point-of-impact between the reticle’s “plus-sign” markers than with the aimpoints within the “plus-signs”.  However, as I moved my target to different distances, I soon noticed that the trajectory was still rising and I soon ran out of scope markings ABOVE the main crosshairs.  Using Chairgun Pro’s “Optimum Zero” function, I selected 37-yards as my next distance for my zeroing the Sightmark Core SX scope.  Chairgun Pro estimated a 1-inch “killzone” from 10 yards out to 40 yards.

Having used scopes in the 12+ power range for years, I was shocked how little adjustment (holdover) was needed with a 3x scope!  
Speaking of bullseyes, I did not have any trouble seeing ¾ inch stickers at distances up to 40 yards.  At 50 and 60 yards I switched 2 inch splatterburst stickers for better visibility and perhaps better consistency. ​​

The most fun (and probably meaningful) test of the day was placing cardboard targets in the snow at distances of 10, 20, 30, 40, 50, and 60 yards.  Each  target had two aim points.  At each distance, I would first aim directly at the left target to see where the pellet was impacting, then I would use the right target to determine elevation correction using the subtensions in the reticle.​

It is worth noting that the reticle’s illumination did start acting up after 200 or so shots.  The scope just decided to turn its illumination on all by itself!  I actually had to rotate the illumination brightness adjustment “on” to actually turn it “off”.  That being said, I did sneak outside in the evening - actually just after dusk - to see how effective the illumination was in dim lighting conditions.  In short besides the on/off issue, the actual quality of illumination was was both effective and pleasing to use.  ​

​Summary (so far…)

In short, this scope has been a pleasure to use.  There is a lot to be said for its relative light weight and size.  It truly matches-up well to the Diana/RWS 48 air rifle with its shorter length-of-pull.  The scope’s clarity is great and this certainly contributes to it's ability to be VERY accurate out to 40 yards on targets that are ¾ of an inch in size.  At 50 to 60 yard distances a ¾ inch dot is  too difficult to resolve (to this shooter’s eyes at least) to accurately place the point-of-aim.  
​
I will also be performing some comparisons to shooting unscoped with the rifle’s open-sights at varying distances.  Stay tuned!

And 4 months later . . .

​​​After sending many pellets downrange using the Sightmark Core SX 3x32 VXR-L Crossbow scope on my .22 caliber RWS / Diana 48, I wanted to see how I may be able to simplify using this scope in a hunting scenario.  Since real quarry typically refuse to hang out at the distances I specify, I decided to use the goat from the Air Venturi Airgun Metal Silhouette target pack!

Though it looks big, it is not that big:

I have found this little 3X scope to be a great tool out to 35-yards (and in right conditions 40-yards).  Compared to most of my other scopes, this one adds little weight, it has a VERY clear image, and as can be used accurately at distances from 8-yards to 35-yards.  While the distances and sight pictures I mention here are unique to my rifle, its ballistics, and my zeroing distances, they should be fairly representative of other users’ experiences. ​
​
​In my case, I found two aiming-points covered the 15 to 35 yard distances which I suspect are some of the most common distances for backyard hunters.  I have also included a closer distance (8-yards) and the longest distance I felt comfortable shooting my silhouette (40-yards)

​o   8-yards = use second set of crosshairs (set one down from main crosshairs)

​o  20-yards = use main crosshairs

​o  30-yards = use top segment of main crosshairs

It was not that I couldn’t hit the target at 40-yards, but I could not hit it consistently given the lighting I was shooting in.  Additionally, my ability to see the yellow silhouette target during my testing made me expect that might be the upper range for effective hunting.  In the shots I took in this testing, I missed once at 30 yards, and a few times at 40 yards. 
​
In graphical terms:

Which is a pretty simple scheme to remember.
The added "advantage" of a low magnification scope is that it is not easy to forget where the limit of an ethical shot lies.

High magnification scopes makes targets look so big that we may take a shot we really should not have.

After several months of using the Sightmark Core SX 3x32 VXR-L Crossbow scope on my Diana/RWS 48 in .22 caliber I wanted to see how shooting with a relatively low-powered scope was compared with shooting open sights.  I began this round of testing shooting paper targets with the simple goal of sighting the rifle in.  For consistency, I am using the same .22 caliber JSB 15.9 grain pellets that I used with the scope testing.  I’ll state up front that the vast majority of shooting I do is with scopes.  None of my PCP rifles even have open sites!  Because of this, I decided to use 20-yards as a my zero distance for the open sight testing. 

Up to this point my “go-to” target was a 3/4 inch colored dot sticker that is found in most any Walmart or office supply store.  These brightly colored dots just plain work for me.  I can slap as many (or as few) of these on normal paper and just shoot.  However, this time shooting 3/4 inch dots at 20-yards without magnification simply wasn’t possible for my eyes.  It took me less than 5-shots to figure this one out!  I next tried drawing similarly sized black dots with a Sharpie marker.  Nope, not going to work either…  ​

So lesson number one is that my visual acuity is so incredibly used to the magnification that even a 3-power scope provides.  I simply could not make out a brightly-colored 3/4 inch target at 20-yards.  The 2-inch Shoot-N-C target was large enough for me to feel that I could place shots using the open-sights that I hoped to test. 

After going through a zeroing and then shooting targets at 10, 15, 20, 25, 30, and 35 yards, I learned a few more lessons!  
One: the amount of adjustment / compensation needed in my sight picture is absolutely minimal.  Where I could use distinct parts of the crosshairs in the scope for repeatable aiming, I found myself measuring changes in “smidgens”…  as in “place the post a smidgen higher”.  
And two: even a 2-inch target is small at 30-yards!  
Three: The harder you look at your target, the more “evasive” it becomes.   I think the best way to describe this is to analogize to stargazing.  Have you ever tried to look at a faint star only to have it hide from you when you try to focus on it?  To see it you almost have to look just to the side of it.  While the effect was not quite as dramatic as stargazing, the target does seem to get more evasive the longer you try to look at it! 

Here are my sample targets where I was compensating for the trajectory.  There are three shots on each target.  As you can see my “smidgen” adjustment for closer distances (10 and 15-yards) still placed the shots a bit high.  The 20-yard target was my zero and 25-yards was just as good.  But you can see my “groups” falling apart at 30 and 35 yards.  Based on this I would limit myself to 25-yards when hunting with open-sights. ​

This is the normal view of a 30 yards target:

Now, some detail focusing on the target:

And what it looks like when focusing on the front sight (as all handbooks say):

​·        15 yards = two misses (high) before hitting it

​·        20 yards = hit

To be blunt, I found the holdover at closer distances was tricky!  And I was shocked that I was able to hit the goat at the longer distances.  There is ZERO chance of me actually placing a shot much past 20 or maybe 25 yards without magnification.  And it’s really quite amazing what a lowly 3x magnification actually does for you!    See pics of each shot at these distances.

In conclusion,

This has been an awesome project to work through!  More than anything else, doing this has reinforced the benefits that even a low-magnification scope brings.  Namely, repeatable aim-points and added “resolution” of your target.  I would encourage every reader who has a pellet gun with open sights to spend a few days shooting without your scope.  It will give you both a new appreciation of those who have gone before us who did amazing things never having a scope, you get a feel for what your rifle may feel like when it sheds the weight of your scope, and it’s fun!

The flip-side of this is a bit more practical.   In my opinion, this modest crossbow scope is an AWESOME tool.  It really does have a great image and adds little weight to you gun.  Most importantly, it WILL allow more accurate shot placement with a minimum of fuss.


Matt Coulter