In VERY FEW cases, we know EXACTLY how, why, where and by whom a word was created. Serendipity is one of those words.
Although it is now widely understood as having to do with luck of some sort. In the original meaning it meant the capacity of making fortunate discoveries seemingly by chance but, in truth, due to acute observations of reality and, possibly, a good memory.

A few months ago, a friend asked me to get his D54 up to snuff for Hunter FT. I told him that I was no longer accepting unknown project guns without an Analysis and Diagnostic phase, because in many occasions, I had undertook a project only to find out that the gun was neither as pristine, nor as accurate as the owner / purchasor was led to believe.

This may have put him off a little because he dropped the idea of having a professional work on the gun and tackled the gun himself. So, a few more months passed.

Suddenly, I get this Email that said that he had played with the gun and he simply could not make it shoot as he thought the gun should. He had changed springs and guides and tried several pellets, but no matter what, the gun shot between 9 and 25 mm's at 30 meters using Exacts 8.44's/4.52's @ 925 fps.

Again, the same "spiel" about the need to get a full A&D phase scheduled and budgeted into the project, only that this time, he took me up on the offer.

And so, the gun arrived. A nice 54 of "intermediate" vintage. T-01 trigger on one side, but the modern round-bellied stock of the current series.

The first thing I did was to chrono the gun when it got here. Lo and behold, the MV's were all over the place! 

A consistent MV (within 17-20 fps in 0.177" cal. or 25-30 fps in 0.22" cal. maximum spreads) is necessary to get good accuracy. It is not a sufficient condition, however. Many guns have produced spectacular chrono strings only to disappoint at the target. 

This gun, however showed extreme spreads of 40 fps (out of 900); this was too much, and even just blowing with lung power into the barrel at both piston positions (cocked and uncocked), showed that the piston seal and the breech seal were leaking. Tore apart the gun and went through a complete re-seal. While the gun was apart, it was clear that someone had attempted a "tune" with a hone/polish. The battery of tests for compression, resilience and rail speed of the piston proved very enlightening. We could now ascertain that the gun would not shoot the heavies fast enough. Remember, up to this point I was trying to follow conventional wisdom and experience that tell us that pellets do not fly well at speeds much higher than 875 fps..

At this point in the story, winter fell on us with a vengeance, and so we tried our best to keep going with whatever short range tests and tools we could.

While giving the barrel a really good cleanout, I detected that the gun had a 'largeish" bore, so some tests were conducted with 4.53 mm's headed JSB Exacts that I always have some around, thanks to Bori at Top Gun Airgun and, yes the diference was quite amazing. The groups started to behave like groups, not patterns.

As soon as the weather allowed, 32 meters testing was conducted, the results are here:

You can clearly see how the 4.53 pellets yield better results.

BUT, what about other pellets?

Short range tests had pointed to the interesting possibility of using JSB Expresses. At 7.9 grains, these pellets have demonstrated pretty good BC's and are reasonably accurate at WFTF levels, being the preferred pellet of MANY of the shooters at the top but, again, common wisdom and conventional thinking told me that this gun at full power could not possibly be shooting the Expresses well.

Still, a scientist will not rest till the rule, or the exception, is proven, so we shot a few groups with Barracuda Match 4.53 and some with Expresses (labelled Xp's):

Some groups were better than others, but in general, the Expresses showed very good accuracy at 32 meters.
When I chronoed the gun I was surprised to see that the gun was shooting the Xp's at 993 fps with a standard deviation of 4 fps for 17.3 ft-lbs of muzzle energy.

So, the questions became ¿WHY?, ¿HOW?  This seemed to go against all experience.

Well, the first step was to capture a pellet from the gun without further deformation. It was important to register what FINAL SHAPE the pellet had acquired after being fired at that speed.
Since my experiments of "Deformation upon Firing" of some years ago, I had not captured too many pellets, so I fished for my capture tube, found it and set it at 20 meters.


Here is what we found when we unraveled all the Dacron fibers:

Clearly the pellet had "Blown Out" but still retained basically a good shape. Waists had also "fattened" up a bit

To give you an idea, Xp's waists usually grow HALF what they grow in this gun when shot at 12 ft/lbs from most guns; from 0.128" to 0.130" . This rifle showed double that deformation, but still retained the shape of the pellet. BOTH this things were conducive to good accuracy.
Now, WHAT was providing that back force to allow the pressure to build up inside the compression chamber so as to cause this "upset" of the projectile, to use the proper ballistic term?

The answer is in the photo. The rifling is not quite the Diana standard rifling. Such deep, narrow grooves is not what we normally expect.

My THEORY is that this barrel was rifled TWICE.

We need to work more with this because it is a very interesting occurrence. Perhaps it is a fluke, perhaps it is not. But definitely this merits some really serious ballistic work.

Now, regardless of the accuracy, the BC DID SUFFER. From the normal 0.021 and upwards (some WFTF shooters report BC's as high as 0.026 for the Xp's from their barrels) to what was actually measured in this case of 0.018 the difference is small, but not negligible.

However, we must not loose sight of the PURPOSE of the rifle. This is a Hunter FT rifle, and so a very high BC is not as desirable as a high MV is.

Analyze this graph:

The Red trajectory is the Xp's at 993 fps. The Green trajectory is the JSB Heavies at 840 fps, the Blue trajectory is what WFTF shooters would hope to get from their rigs and is only there for comparison. On the right hand vertical axis we have the divisions corresponding to a ¼ mrad spacing. On the left vertical axis we have inches of drop.

All trajectories have been maximized for range. All setups are identical in scope height.

Our shooter is shooting HFT, so his Scope is 12X, but there are good scopes that offer ½ mrad at 12X, so that allows us to use ¼ mrads for rangefinding and for holdoff's. With ¼ mrads our range estimating error by bracketing can be of up to 4 yards at the max range. This means we could mistake a 55 yard target for a 51 yard target (based on the common dimensions found on targets).

So, if the error is 4 yards, and we shoot a 55 yard target as if it was a 51 yarder, that means that the shooter will estimate the 2nd ¼ mark down, which would be correct, but the target is really at 55, so the shot will land ½" LOW, BUT since at this range the minimum KZ size is 1.5", it means that his shot should still land within the KZ.

Now, the WIND . . . is another matter altogether. But there are much better probabilities of being able to rangefind well than to estimate wind well. So, that is why we look for the most advantages in the ranging.

Overall, it was a VERY interesting project and it shows an interesting avenue of research into rifling designs.

Keep well and shoot straight!


HM

Some days ago a friend asked:  "¿why 'de-tune' a large airgun to obtain the performance of a smaller one?"

We were talking then about the Diana 280. A small, handy carbine that was designed from the ground up to yield 12 ft-lbs. Sort of a "short action" D-34.

I obviously understood what he was referring to by "de-tune", but then it struck me that the specific way of putting it was very American.
If you "tune" something it is to get more power out of it, ¿Isn't it?, ¿how could there possibly be ANY other understanding of the verb "to tune". At least within the airgunners' circles.

That exchange prompted a train of thought that carried from my insistence in "tuning for optimal stability", to the sometimes jokingly expressed recriminations about issuing D-54's at "NERF gun level" of 12 ft-lbs.

Since there is precious little I can do for the time being between the weather and my health, I decided to dig on my records, do a little bit of experimenting (not much, mind you), and then respond with some facts.

Usually, when I build a CCA WFTF D-54 "engine" (understanding this as the metal powerplant heart of the house section of the gun), I have to cut off 2 coils and change from full power springs. 
¿Why? 
To answer that we need to go back to how the Int'l HMO Piston was designed. 
Back in 2007 I was designing the piston to yield at least 12 ft-lbs when used in Latin America. 
Latin America has a number of country capitals that are above the 7,500 feet above sea level range.
Piston airguns do not have their own air supply, they work with whatever is available in the environment.
Experience had shown that at that altitude, power output was reduced to about 84% of what could be obtained between sea level and the first 1,000 FASL; so the piston was designed in such a way as to yield 14 ft-lbs. at sea level. 
Some calculations and a little final tweaking yielded the current spec for the Int'l HMO piston.


So, what CAN you get when you put an Int'l HMO piston in a D54?

I gathered some data, ran some experiments, and these are the results:

As you can see, it is fairly easy to reach the maximum velocity/stability region of normal skirted pellets, either with the springs "as is" or with about ½ the maximum spacing available.
Cocking effort of all these setups was under 23# of peak force.

It is important to mention that even with 13 mm's spacing up, the spring is much less stressed than the OEM arrangement where the stroke of the OEM piston requires a compression of a full 100 mm's. So expected life of the spring should be quite interesting. Perhaps not the 20-30,000 rounds of the least stressed WFTF version, but interesting none the less.

¿Could you get more power?
A little, yes, but the spring is fast approaching the region of diminishing returns.

In this context, if someone absolutely WANTS to shoot heavy pellets, the full stroke gun is the only option. 
I emphasize the word WANT because when you "tune" for stability, the BC of the 8.44 pellet approaches real fast the BC of the 10.3. Thereby negating the perceived advantage of the heavy pellet either in trajectory or in wind deflection.

In most instances I've seen in the field, driving hard the 10.3 pellets usually yields BC's that are inferior to the lower weighted projectiles driven to reasonable speeds. And by driving hard I mean that even a very capable engine like the D54 is not really made to yield more than 17½-18 ft-lbs in 0.177" cal. which means a 10.3 grs. pellet having a MV of 875 fps. Not as an airgun. Guns that yield more than that are usually dieseling to different degrees and that, again, usually carries over an increased probability of pellet deformation upon firing, which will degrade the BC of the pellet in flight; and inconsistencies as fuel is burned up.

In larger calibers, up to 0.22", the engines are quite capable of delivering more power due to an increase in Expansion Ratio.

For anyone looking for a nice, steady, easy to use "Hunter" rifle, I would think it hard to find something that can cock as easily, return as much energy per lb of cocking force as these setups do, and be as consistent as the good old D54.

Sorry I cannot post targets; with so much snow I found it impossible to do any testing.

Do NOT put too much emphasis on the uniformity of MV's. As long as MV's are within an extreme spread of 15-17 fps, which SHOULD translate into Standard Deviations of 5-6 fps. you should not worry too much. I've seen too many rifles shoot very uniform MV's just to be disappointed at the poor results where it counts: AT the TARGET.

Keep well and shoot straight!

Everyone thinks that the only thing that the Swiss have invented are Cuckoo Clocks, wristwatches .  .  . and maybe banks, but that is far from true; among other things, the Swiss have to their credit a number of innovations in the science and weapons fields. Obviously when you are a tiny nation in between military powers like Germany, France and Italy you'ld better be VERY well prepared if you want to keep your independence for more than 1,000 years.

Anyway, among the things that military science developed in Switzerland is the milliradian. The root of the "Mil" section in "mil-dots". It was invented by Charles Marc Dapples, around the late 1800's, and by 1914, more than a few countries had already adopted it. France being the first one, as it needed a better sighting and ranging method for their "75" the first truly worthwhile field artillery piece.

Later, in the 1950's NATO standardized to metric units and the milliradian became the standard unit of measure for angle.

So, exactly WHAT is a milliradian? Well, a milliradian is the 1/1000th part of a radian, and before you say: "Dooohhh", let me explain that a radian (rad.) is the angle subtended when the LENGTH along the circumference is the same as the radius of said circumference. This curious definition defines an ANGLE using a CURVED line and a straight line. ¿WHY?, well, Monsieur Dapples was a mathematician and an engineer, and he liked absolute precision in concepts but practical ways for applications; because the relation between a circumference and its diameter is the number "Pi" (also expressed as the greek letter π), that is an endless number, he wanted to be precise but he did not want to write the digits of one number for the rest of his life. So, by using "π" , he was at the same time, scientific and engineering. He was expressing the EXACT relation, but for engineering calculations (slide rules in those days, no calculators and, even less, computers), he could approximate very well (all engineering slide rules have π marked in the scale). So he "discovered" that under the definition of his "radian" as an angle unit, the circumference had 2π radians (remember the circumference of a circle is π x diameter, and that the diameter is twice the radius, so the whole circumference measures 2πr), or ≈ 2x3.141592652xr

From the above, you could say now that if 360º= 2π, then 1radian≈57.2958º, or that 1º≈17.4533 mrads

Up to that point, the UTILITY of the mrad lies only in the manufacture of clocks, where gears and gears and more gears are used to divide the time into the smallest pulsations possible, thereby enabling the clock or watch to be more and more precise; BUT, ¿HOW did the mrad jumped to artillery and then to riflemen usage?

Well, we need to understand at least ONE concept of trigonometry: the sine.

Before you get scared, look at this picture:

It is a simple "right" triangle. It is called "right" not because all other triangles are "wrong", but because ONE of the angles is 90º (or a "right" angle). In the picture the greek letter Θ ("Theta"), stands as the name of the angle we want to work with, and because the angle is a CONSTANT RELATION between the LENGTHS of the Hypotenuse and the opposite sides, then knowing this proportion allows us to "scale" up and down the triangle and ALWAYS keep the same relation between those two lengths. Conversely, if we KNOW the VALUE of that proportion and we know ONE of the lengths, then we can calculate the other. 

One of those relations is called "sine". And it is defined as the length of the opposite divided by the length of the hypotenuse:  

sine(Θ)= opposite/hypotenuse

Now, imagine that the opposite side was a section of a circumference whose center is the corner where the Θ letter is located, it would not be straight, but it would have a length. If that opposite side was the SAME length as the "nameless" side in the diagram (usually called the adjacent, but let's leave it as "nameless" for fun), then the LENGTH of the opposite would be the SAME LENGTH as the radius that generates the opposite (the "nameless" length), and then Θ = 1 rad.

Now, here comes the magic, and because I do not want to bore you with more maths, let's look at a table:

As you can see, expressed in more conventional units:
sine(90º)=1.000
sine (75º)=0.966
sine (60º)=0.866
sine (45º)=0.707
sine (30º)=0.500
sine (15º)= 0.259
sine (0º)= 0.000

BUT (always a big BUT somewhere!, LOL!), when expressed in radians:

sine (90º≈1.57rads)=1.000 (difference between rads and value of sine = .57)
sine (75º≈1.31rads)=0.966 (difference = 0.34)
sine (60º≈1.05rads)=0.866 (difference = 0.18)
sine (45º≈0.79rads)=0.707 (difference = 0.083)
sine (30º≈0.524rads)=0.500 (difference = 0.024)
sine (15º≈0.262rads)=0.259 (difference = 0.003)
sine (0º=0rads)=0, difference ZERO.

We therefore KNOW that for SMALL angles the angle in rads and the sine of the angle have almost the same value because we have analyzed that the differences become smaller and smaller.

IF the angle in rads (or millirads, to use the "zone" we are talking about) has the same value as the sine of that angle, then the original definition of sine above:

sine(Θ)= opposite/hypotenuse

Can also be expressed in more useful terms: Hypotenuse = Opposite/sine(Θ)=1000 x Opposite/mrads

If we translate trigonometric terms to shooting terms then:

Range = 1000 x (known dimension of target / mrads) and the mrads is what we measure with the marks of our scopes' reticules (when the reticule is either First Focal Plane, or set at its "true" magnification).

For example: If I know that my target is 1 yard high (a small Roebuck) and the whole animal can be fitted between the centers of two consecutive dots, or between two consecutive unit hashmarks, then I know that buck is 1,000 yards away. If said buck occupied TWO dots, then it is 500 yards away, if it occupied 4 dots, then it is 250 yards away (now it is a doable shot at such small quarry).

Of course, if I know that my zero is at 250 yards, then I can take the shot with "no hold" (either over, under, left or right), but if I know where my trajectory is at all distances, then I can hold to the EXACT point where I KNOW I will hit the target. I can ALSO allow for wind.

This is the "principle" of bracketing, this is WHY it works. There are plenty of writeups in the web about the usage of mil-dots in different units, different configurations (Army vs. Navy), different reticules, formulae and even places where you can buy the modern version of a specific slide rule, called the Mil-Dot Master that makes Imperial Unit users get the numbers right. 
I will not go there. For me it is dead easy because I am metric and in metric units if you express the height or width of an object in milimeters, and use true dots or hashes, you get directly the range in meters.

What is almost non-existent in the "Imperial Units" shooting literature is how to measure, set, or ensure that your mil-dot scope (or variations thereof) IS truly useful, or not. So let's get into that, using one of the excellent AEON scopes, an 8-32X50:

Because the relation between range and target size starts from a basic relation of 1:1,000, you need to find a place where you can set a construction ruler (one of those squares/rulers that are used to mark and and cut gypsum board) at 83 feet and 4 inches (83' 4"). ¿Why that specific distance? simple! there are 1,000 " in 83' 4"; and the rulers and squares we are talking about come marked in inches and fractions thereof.

So you need to setup something like this:

At the "target" end you need something as simple as this:

After setting up with the metal tape, I always reconfirm the LOS distance with a laser distance meter (not a shooting rangefinder, a laser distance meter or laser measuring tool) because there is no way I can hold the tape taut enough to ensure that the distance is truly what I need when I work alone. Perhaps doing this with a buddy might enable you to hold the tape taut enough. Then you sight in and focus your scope:

If you are famliar with the scope brand and reticle design, then you know more or less where in the mag ring the scope's reticle will be "true", that is a good starting point.

And then you fiddle with the mag ring till the most extreme marks in your reticle align with the inch marks in the ruler. Sometimes it takes more than a little fiddling, but patience here will yield huge rewards later, as you will be CONFIDENT of what you are measuring with.

As you can see from this picture the top hashmark aligns with the 34" marking on the ruler, the next full unit mark aligns with the 33", then the "zero" aligns with the 32", the next full unit down aligns with the 31", the next down with the 30" and the last one with the 29" (when doing precision work use one SIDE of the white line marking in the ruler, as opposed to the center of the -usually- thick line, this will ensure better consistency).

Do note that in this scope, the sizes of the marks are VERY consistent, even across half of the field of view of the riflescope.

This is not common in "economy" scopes and it is one of the reasons why we like the AEON brand of riflescopes.

Also note that for every full unit mark, the AEON scopes have 4 intermediate marks, thereby allowing us to measure not only in mrads, but in ¼ mrads and estimate up to 1/8 mrads.

The greater resolution in the measurement AND in the hold-off are very important in Field Target, especially when shooting in the southern clubs of the US of A that love tiny Kill Zones.

In case you have one of the economy scopes that are "true" at 10X, but you have, at least, up to 12X magnification in your zoom ring, you still have one more thing you can do:

First ensure that your reticle is TRUE at 10X using the above procedure.

Then move the ruler to the 100' line and set your magnification at 12X, you SHOULD see that the dots in the reticle and the inches in the ruler coincide. This is because at 12X, the reticule is no longer mrad, but it does measure IPHF (Inch Per Hundred Feet) angles, and the approximation of sine to length still works. So you CAN use your 12x/true at 10X scope to do the ranging and the hold, BUT you need to ensure that the field of vision is FLAT (the last distance between dots measures the same as the first one), and you would be wise then to use your range card in feet, not yards.

Hope this helps!






HM

There is a ton of misconceptions about what REALLY is the B.C. (acronym of Ballistic Coefficient) of a projectile.
Probably, the most noxious one is the one that equates a high B.C. to a "good" projectile and a low B.C. to a "bad" projectile.
B.C. is NOT a measure of the "design qualities" of a projectile.

So. . . . ¿What is BC?

First and foremost, BC is a SCALE FACTOR.

To explain this we need to go back almost two hundred years, to the heroic days when small, field worthy artillery pieces were truly coming into their own. When smokeless powder first became a commercial and military reality, and when the value of a soldier's life was less than the value of the musket he carried.
So, imagine yourself living from the 1840's to the late 1880's:
The US has just doubled its territory by waging war on México.
Crimea has just been lost by the Russians to a Western European bloc
Germany has just annexed all the Alsace Lorraine
The French have just invented the "75" and Captain Dreyfus is spending some time in "Devil's Island" because it is easier for the "Establishment" to send an innocent person to his death in a tropical island than to accept that the ring of spies is so well entrenched in the government circles as to make it a "Reason of Sate". 
Russia is trying to assert its role in the "modern world" and the Czar decides to support the Army because supporting the Navy, with no warm water sea port is senseless. There is a peculiar alliance being established between France (the 3rd Republic) and Russia (an Imperial Autocratic State).

Out of England (THE Maritime Power of its day), comes a young chap by the name Francis Bashforth; developing on the (by then 200 years old) ideas by Benjamin Robins, he creates in the late 1860's an electromechanical chronograph that is capable of measuring velocities of projectiles to much greater precision than the ballistic pendula of the day. Consider that to measure ACCURATELY, a ballistic pendulum has to have a mass at least 200 times greater than the projectile it tries to measure. Now consider the size of ballistic pendula for artillery ogives.
Bashforth measures and creates tables for all his measurements, and then comes up with a flash of brilliance:
¿What if ALL the effort was devoted to a "standard" projectile, could he then prove that all other projectiles would have a SIMILAR behaviour? 

Similarity, in the mathematical context, is the capacity to change one thing into another using a scale factor.

And so, he proposes the Ballistic Coefficient; a SCALE factor that can tell technicians how a given projectile will behave BASED on a LOT of firings of a STANDARD projectile.

Being a good Yorkshireman, and VERY British, Bashforth uses a Standard Projectile (S.P.) of 1.00" Caliber, with a 1.5" tangent Ogive, weighing (¿What else?) 1 lb. And this becomes the B.C. = 1.00

Now, let's come to the present and analyze this a little: ¿What on earth can be MORE DIS-SIMILAR than a flat base, 1.5 calibers tangent ogive, parallel sides projectile, weighing all of 7,000 grains in 1.00" Cal. AND an 8.44 grains, diabolo shaped (waisted) pellet with an ogive barely 1.25 calibers in cal. 0.177"?

Caliber of the S.P. is more than 5½ times the caliber of the projectile we are interested in. 
Mass of S.P. is more than 800 (eight HUNDRED) times the mass of the projectile of interest.

There is NOTHING of the S.P. that barely resembles our pellets. How can we HOPE to use a simple SCALE factor?

Well, we can't.

And neither can do many others interested in the exterior ballistics.

Going back to the late 18th Century, the Russian Mayevski, then the Italian Siacci and then the American Ingalls, conducted a LARGE number of tests. At the same time, Krupp was conducting their own experiments and by 1875-1890 all nations had a pretty well informed knowledge of what exterior ballistics truly meant, as far as field artillery pieces were concerned. Just in time for the Balkan Wars, and then World War I.

Let's get this chart clear. The chart illustrates how the DRAG changes with speed. It is NOT a B.C. change chart, but it is close in an inverse sort of way.

Now, please consider: IF drag changes like this for every speed along the pellet's projectile, then the B.C. that is trying to scale a whole trajectory is much more dependent on how closely the projectile of interest is to the S.P.

It was the Russian, the Italian and the American, the ones that first proposed a DIFFERENT way to look at things: ¿Why not develop a mathematical model that, taking into account the physical characteristics of the projectiles will give us firing solutions?

Ah! that sounded GREAT!, let's call it Drag Function and then we can PREDICT what things will behave like as long as we know how those physical characteristics relate to the external ballistics.
At first it seemed that a "form factor" could be established that related the B.C. to the sectional density (the weight of the projectile -in lbs.- divided by the square of the caliber), BUT then the form factor became something to be qualitatively assigned. Tables were prepared where by graphical observations, shooters could ascertain which form factor they could use for their bullets.

REAL problem is that reality is a little too rich in details and too complicated to actually be able to do this with any really good precision. Few functions are linear, and since the old days, the exterior ballistics solutions have been, in reality, approximations by velocity regions. One set of equations, constants and coefficients apply from 0 to about 850 fps, another from 850 to about 1,100, another from 1,100 to about 1,400, then another between 1,400 and 2,200, and another between 2,200 and 5,000 fps.

Even at present, military applications use one Drag Function and commercial applications use another.

In the market there are several programs and types of software that use the drag coefficients. BUT they all have the same caveat: Use only by sections and make sure that YOUR case is not close to the boundaries of the sections. A few really good and conscientious manufacturers publish the B.C.'s for their bullets by MV regions.

In more recent times, with the advent of cheap and relatively reliable and precise chronographs, it has become easy to determine the "deceleration" (loss of velocity) of ANY projectile, and there have been some rather interesting approaches to solving the firing solutions. 

Among the more imaginative is Pejsa's "Velocity Retention Factor", and similar approaches whereupon some of the modern airgun pellet ballistics programs work.

Another aspect about shooting pellets as opposed to bullets, is that our pellets deform upon firing.
The BEST mathematical model taken from the dimensions of the newly produced pellet will NOT be true once you fire that pellet through ANY barrel.

Modern pellets and modern barrels do this less dramatically than those made only a few decades ago. Compare the above picture to this one:

And, I think it is obvious, but I will say it again: EACH pellet/barrel combination will do this in a slightly different manner.
So, there is NO way to use a "table" B.C. for your pellet calculations, if you want them to be precise.

One of the peculiar differences between airgun shooters and powder burners is that, for them, some differences are "small" or "inconsequential". For airgunners where the targets are measured in fractions of an inch, there is no really inconsequential difference. 
Especially for FT shooters. 
A 40 Troyers target (a measure of relative difficulty) is a ½" target at 20 yards. The pellet occupies 0.177" of that, so the real wiggle room is about 0.32" If you consider that the pellet needs to be LESS than one caliber off to any side from center, you realize how accurate FT shooters and gear have to be.
And that is not the hardest target in an FT course, Match Directors can place these ½" targets all the way out to 30 yards! for a 60 Troyer shot.

Anyway, coming back to B.C.:

It seems to be one of those things that you are bad with it, and even worse without it.

For years I used Pejsa's approach and tried to calculate and keep good records of Velocity Retention Coefficients for all pellets in all my rifles. And then we went to Norway to shoot at the FT World's Matches and  I got faced with wind drift.

This is the OTHER side of B.C.: ONCE YOU HAVE A TRUE B.C. then wind DOES become a scientific calculation.

Not only that, Wind drift is proportional to normal velocity (velocity vector measured perpendicular to the trajectory plane). So, if you could have the B.C. for YOUR pellet, shot from YOUR rifle, at the place you ARE shooting, then wind drift is really more a matter of learning how to "guesstimate" this normal wind velocity.

BUT. . .  chicken and egg situation! How can I find the B.C. of my pellets shot at places as dis-similar as Norway (coastal location), Germany (mountain location), Texas (lowland, dry location), or Baton Rouge (humid, coastal location). ¿Should I take my two, matched, Chronos and do all my testing all over again?
¿At EVERY venue?

Well, enter a different point of view and a recently modern mathematical approach called "Fuzzy Logic", where one quantity can have not only A value, but a RANGE of values. Then you go on the next "test case" and check that range of values against the new one, and by discarding those values that are OUTSIDE BOTH ranges, you have a narrower range. Then you take a THIRD test case and come up with a different range of values, when you compare all three and come up with the value that meets all three test cases, then you have your solution.

This is how P-P Calc works.

And that is why I came back to the B.C. method. By using a zero range and THREE more ranges and POI's, the software calculates the B.C. by sections of the pellet path, it will give you a weighted average and use that for the calculations, but more importantly, it will calculate the wind drift.

While discussing the error in B.C.'s  vs. the Wind Normal Velocity reading error with a very good shooter, Scott Hull, he came up with this example:

As you can see, an error of 0.006 in the B.C. (six thousandths, from 0.021 to 0.015) will move your POI as much as an error of 1 mph in reading the wind.

As much as we dislike the idea, we cannot fault our pellets for having such a low B.C. (just to illustrate, some modern 0.50" cal bullets have B.C.'s GREATER than 1.00)
The low B.C. is what makes the use of our pellet rifles relatively safe in urban environments and at close distances.
The low B.C. of our pellets is what gives us the same challenge shooting out to 55 yards as the H.P shooters get shooting at 600 yards.
The low B.C. of our pellets is what makes our sport unique.

In conclusion:
Pellet shooters CAN use the B.C. concept, but they need to be careful to apply it by sections.
"Fiddling" with the B.C. is not too smart unless you REALLY know your rifle/pellet combination well. You may arrive at a scale factor (the B.C.) that has nothing to do with reality.
P-P Calc will allow you to MEASURE the B.C. from YOUR rifle/pellet combination at EVERY venue. You can then store that venue for future reference.

Hope this has been informative and I hope to see you at some FT Match soon!







HM