"Blue-Printing" a Walther LGV ©

5/24/2022

In "gun-speak" blueprinting an action is understood as the modifications/alterations that make that action fit the specified dimensions of the design.

In this entry, we will use the verb as meaning that we are returning the rifle, as much as possible, to the "as it SHOULD HAVE BEEN issued" state.

It all started quite some months ago (Pre-CoViD) when I was contacted by a fellow FT shooter asking what was the potential in using a Walther LGV to shoot FT.

Since an LGV is my "back-up" gun for serious FT, I answered that a properly setup rifle could be accurate, precise and consistent enough to place well in a competition.

After that first conversation, there was no more talk and I thought that the whole idea had been forgotten.

BUT, in the last North Carolina Classsic, I met with the friend in question and after the first day of competition, he declared: "I'm done, take the gun and make it what it can be".

So, I came back with more guns than I took! LOL!

I will not go into detail about the tear down and the way the gun works, there are other entries that deal with that:

https://www.ctcustomairguns.com/hectors-airgun-blog/a-yankee-tune-for-the-walther-lgu

https://www.ctcustomairguns.com/hectors-airgun-blog/a-yankee-tune-for-the-walther-lgu-second-version

Since the guns are identical, except for the cocking mechanism, what is said of one gun applies to both.

What was the difference this time as regards those first ventures into the LGU/LGV realm was that on this occasion I had NO IDEA of the provenance of the gun. It was an LGV Master. And I am sure it was bought in the USA, my friend purchased it "from a gentleman in PA", but that still does not justify what happened.

So, let's get into the project.

The Rifle.-
My friend is a good shooter. He is, literally, Championship material, so if he says the gun is inconsistent, I tend to believe him, but inconsistent by how much was still a question, so . . . the first thing was to put the gun through the Chrono.
Testing with JSB's 8.44 grs./ 4.52 mms, gave horrible results, in a 20 shot string the ES was 27 fps for a Low of 735 and a High of 762, for an average of 750 ± 7 fps for 10.6 ft-lbs
CLEARLY something was wrong.

On disassembly, I noticed that the previous owner had applied the "Yankee Tune" principles to the "Tee". But the gun simply refused to yield the energy promised and even some drastic spacing forward and aft, did not provide the desired results.

Vortek unit with added spacers

It was also obvious that some effort had been made to tame the buzz through the liberal application of greases:

Gobs of grease

Complete disassembly showed the rear part of the powerplant train:

Rear Section of Powerplant

And I still had to find the heavily spaced TopHat which was hiding inside the piston.
The seal wasn't either an OEM one, being blue, slimmer and shorter than the original:

Non-OEM seal is slimmer

OEM seal's Bore Diameter

Rear Gap with Blue Seal

Piston with Blue seal is shorter

If the idea was to add a millimeter of stroke to the compression volume, the advantage was lost with the looseness and the gaps.

The Fix.-

Still, the job was cut out and so, I replaced all parts for OEM parts (as wished by the owner):

Full OEM Powerplant

A new piston, a new guide and a new spring were installed, all OEM parts.

Observant readers will note that the OEM trigger has been replaced! Yes that is one of Eric Pianori's triggers:

https://www.ctcustomairguns.com/hectors-airgun-blog/new-super-custom-trigger-for-the-walther-lgulgv

and it is superbly adjustable, consistent and reliable.

I thought that everything had gone "just peachy" till the chrono test:

With the same JSB's, the gun clocked 741 ± 4 fps

WHAAATTT?

Uhh-Ohh! I guess that, by now, I should KNOW that if a gun gets to me, it is because others have not found a way to make it work as the owner/customer wants, or as the gun is expected to perform.

Reading over some of my notes, I remembered that at one point I had refused to change the TP of an LGV, preferring to use a much more complicated solution:

https://www.ctcustomairguns.com/hectors-airgun-blog/the-walther-lgv-pushing-the-power-limits

But the owner, in THIS case wanted to have the gun "blue-printed" and nothing is as non-OEM as a custom piston.
It had also happened that I had HAD to open a TP in some other break-barrels and I had made the tools to do it properly, so this time around, I did have the wherewithal to tackle the TP enlargement.

In brief: you need carbide drills to drill out the TP to the dimension you need/want, and also a way to remove the drilling burr from the INSIDE of the compression chamber that results from drilling from the outside in.

Carbide drills will cut a VERY precise and smooth hole in steel at slow speeds with mutton tallow lubrication, and that gives you control of the process, it also produces little burr on the other side of the drill, important when the "other side" is, in reality, the INSIDE of the compression chamber; where another surprise awaited us.

Deep Drilling Setup

Peeking into the Face

As you can see there is a gap between the end and the sidewalls of the compression chamber, where a ring of "gunk" forms. You can also see that the face/end of the compression chamber is not perfectly flat.
This gun will never achieve true "full power" because there is a "lost volume" that we cannot get rid of. A lost volume that even the excellent OEM LGV "power pulse" style seal cannot remediate.
It could be fixed with a custom piston, but then that would not be a "blue-printed" gun.

The other thing you can see in this picture (or better yet, you CANNOT see), is the normal burr from drilling the TP out from the OTHER side.
A larger drill was applied with the extension shown above and the burr removed.
Some have argued that the inside of the TP's should be "venturi'ed", IMHO, that is counterproductive because when air flows at the speed at which it flows inside these machines, a slightly turbulent flow is actually a better "lubricated" flow; a venturi style of entry would tend to reduce turbulences, which is something we do not want.
So, we only removed the burr and made sure that nothing was there to damage the seal in the second (or third) landing of the piston.
Here is a detailed look at the TP and surrounding area:

A detailed look of the Face

So, with the TP drilled out to the MINIMUM required for the 12 ft-lbs requested by the owner, we tested different pellets and finally settled on a combination that seems to give very good results.
The barrel in this rifle is easily one of the best I have seen/slugged in any modern Walther, and it seems to prefer the lighter spectrum of pellets (7.9 grs), shooting them at 827 ± 4 fps for 12 ft-lbs on the dot (and the innards are still in the "running in" phase). Predictably, this rifle will settle in the 835-840 fps average and the extreme spread in MV will be reduced to single digit.
This rifle is destined to shoot AAFTA style Hunter Division, so a little over 12 ft-lbs is no problem at all.

The results.-

To test this gun I installed a SIGHTRON 4-12X40 AO scope that has proven to be VERY reliable in an Accurized ZR mount:

Complete view of the LGV rifle

It was very nice to just mount the scope and to have no need of further regulation to get the rifle sighted in at the optical axis of the scope. And so, after some short range tests to determine if the JSB Xp was the right pellet and confirming that it was, I adjourned to the 25 yards distance and this was the result (target shot from the bottom, up):

25 yds Test

As for the non-OEM part, my friend asked for a light and creepless trigger, so I used Eric's trigger's middle screw (to reduce the back force of the spring) and adjusted to a bit less than 1#, this is the average of 5 trigger pulls:

Trigger pull setting

Overall, a very rewarding project, while the gun will not achieve the 17/23 Joules advertised originally, it is still yielding a good performance for the cocking force, and it is working as a "pop gun" in the "Olde English Air Gonne" parlance, meaning that the lubricants are kept to a minimum and there is no energy contributed to the pellet by moderate dieseling.
As ALL Walthers that are made to work in the "pop gun" region, it is a bit "ringy". If this bothers the user the solution is extremely simple: just add a VERY LIGHT coating of tar to the spring. To ME, the thermal aspects of how tar behaves between a cool 50 ° F morning and a scorching 90 ° F noon are not worth it but, to each his own.

There is more to read about the LGV's in this blog, some of the entries have been superseded by newer materials and components, but I hope the readers will find them interesting:

https://www.ctcustomairguns.com/hectors-airgun-blog/swapping-the-walther-lgus-trigger

https://www.ctcustomairguns.com/hectors-airgun-blog/the-walther-lgv-a-second-look

https://www.ctcustomairguns.com/hectors-airgun-blog/the-gunsmiths-tune-part-14-full-power-walther-lgv

https://www.ctcustomairguns.com/hectors-airgun-blog/the-gunsmiths-tune-part-24-12-ft-lbs-walther-lgv

In the meantime, take care, keep well and shoot straight!

HM © May 23,2022

11 Comments

Peter link

6/3/2022 00:39:48

Almagard 3752 Red sticky grease may be better than tar for eliminating spring twang; without inducing temperature sensitivity:
https://www.gatewaytoairguns.org/GTA/index.php?topic=192358.0

Hector Medina

6/3/2022 11:40:06

Hello Peter!

While it is true that some "open gear" greases, such as Almagard are sticky enough to dampen the "twang". It is also true that:
1.- They migrate, get into the compression chamber and therefore add power through combustion. Sadly NOT in a controlled manner.
2.- Once the greases migrate, the "twang" comes back.

Finally, if you look at the MSDSheet, you will see that the proprietary compounds that make this grease so useful in non-combusting applications, MAY become problematic once you reach the 400 F flash point and the metal carbamates are free to enter your lungs.
It's up to each one of us to decide what risks are acceptable and which ones aren't.

Personally, I will go along with a bit of "ringing" in exchange of using time proven and tested Ultimox 226.

Some time ago someone asked if it would be possible to use "Plasti-Dip" to coat the springs and dampen the vibrations. Of course the problem is that you need a PARTIAL coating so that the bare steel rides on the guide, while the rest of the spring is outside coated.

IMHE the best solution so far is the Teflon-based coating of Titan XS springs. It is hard enough to be part of the spring, flexible enough that it will not crack nor chip with use.
And it does a creditable job of dry-lubing the guide to spring interface, as well as dampening some vibrations.

The ONLY caveat about Titan springs is that when you cut, forge closed, and square a spring, you SHOULD use a mask that is capable of capturing the particulates, AND the operation should be done in the open with the best ventilation possible.

Now;
In THIS case, we could not use a Titan spring because the idea was to use all OEM parts.

Thanks for reading!

HM

Peter link

6/4/2022 20:25:37

Ed's method (see link) is the preferred embodiment for removing spring twang: He makes a custom tight fitting spring guide, and uses only Krytox non-combustible grease. It is the right way, while a lube tune is for lazy people in a hurry: https://www.gatewaytoairguns.org/GTA/index.php?topic=199817.msg156334234#msg156334234

As for overheating, even the Teflon in Krytox forms toxic compounds when heated over 260 degrees C (500 F). Such temperatures are easily reached due to adiabatic compression in a "springer". So, the goal is to avoid using so much grease that it tends to migrate ahead of the piston seal, to the extent that some of it is blown out of the transfer port, exposed to the hot air.

Hector Medina

6/8/2022 18:45:09

Peter;

Do note that we are NOT dealing with "Twang".
Guide is tight and lube is Ultimox (the non-hygroscopic version of Krytox), and no, it does not "diesel".

It's the small portion of the spring that is NOT supported by the guide the one that "rings", like a small bell and mostly only perceptible by the shooter that has his face glued to the stock. The outside world does not "hear the ring".

;-)

HM

Arnoldus

6/8/2022 18:10:51

Hey Hector, question:

- "Some have argued that the inside of the TP's should be "venturi'ed", IMHO, that is counterproductive because when air flows at the speed at which it flows inside these machines, a slightly turbulent flow is actually a better "lubricated" flow; a venturi style of entry would tend to reduce turbulences, which is something we do not want."

Can you explain why that is? From the little I understand, a nozzle improves things.
E.g. here it is nicely shown how subsonic air flow is made supersonic to shoot a pingpong ball supersonically (before/after):

https://newatlas.com/how-to-build-a-supersonic-ping-pong-gun/26082/

Hector Medina

6/8/2022 19:30:14

Arnoldus;

C-D-N are peculiar animals.
They are Calculated to allow the OPTIMAL rate of acceleration for a rocket that is flying through the air.
¿Problem? the expansion cone depends on the ambient pressure, and since rockets go from sea level to the borders of the atmosphere and beyond, the shape and curve are a COMPROMISE.

In the ping-pong ball experiment, there is no air in the tube, so the idea of the ping-pong going "supersonic" is somewhat of a brain teaser, if not an oxymoron, because there is NO limit to sound speed in vacuum. In fact sound has no speed in vacuum.

The ping-pong ball flies at Mach 1.2, yes, but is it truly breaking the sound barrier?

Herein lies the MAIN difference between a flow that is driven and pulled (in the case of the ping-pong experiment) and a flow that has to PUSH and push HARD. Because it is not only the inertia of the air that needs to be compressed the one that is obstructing the acceleration of the projectile, it is the weight of the projectile itself, PLUS, the low expansion ratio of the barrel (small caliber, short tube), PLUS the weight of the air that tries to move out of the barrel REAL FAST in front of the projectile.

Under the real life conditions of our airguns, we can only approach Mach speeds in the TP by keeping the pressure up as much as the shot cycle allows us. This raises the temperature and that in turn raises the sound barrier speed.

BUT beyond the TP, things start cooling real fast, mainly because of the expansion of the gas into the ever increasing volume of the barrel when the pellet starts moving towards the muzzle. So the "lower" sound barrier (340 m/s) comes into effect again.

The OTHER aspect is that the TP is substantially longer than a C-D-N would be.

And herein lies an inherent advantage of those guns with sliding compression chambers, fixed barrels and short TP's.
In the case of the super-short TP, the TP CAN be used as a "valve". Allowing high pressure, high temperature, high speed air to enter the barrel, but blocking (at least partially), the return flow when the temperature, pressure and speeds drop.

In fact, I would challenge the Purdue Prof to do the following test:
Remove the C-D-N and re-test the speed with the same vacuum and pressure, see how much the C-D-N really contributes.

For comparison, you can see almost the same arrangement as Purdue's but WITHOUT the C-D-N reach about the same speeds:

https://www.youtube.com/watch?v=msgfm4DHiyc

I think that at times, we put too much emphasis on number of degrees and years of experience in a group, when all that is really needed is some "common sense" .

;-)

Keep well and shoot straight!

HM

Arnoldus

6/9/2022 09:15:25

Thanks for the explanation, I'm don't have a technical background so it's nice to hear from an engineer how things actually work and what the underlying design idea is!

- In the video, the professor says that without the nozzle, the speeds are ca 200m/s for the pingpong ball. So adding the nozzle doubles the exit speed (so quadruples the muzzle energy). That's what impressed me and why I was so curious about it.

- If the TP is a valve: well why don't we have a (small) valve such as on PCP's then? It would also only open once a pressure treshhold has been achieved, making the energy release more effective (not pushing against a pellet which is already moving and leaving a larger volume behind it). Perhaps that could also make slugs work in springers, given they need higher pressures to get pushed through the barrel.

- I understand what you wrote, basically "it's a feature, not a bug". I.e. you design for for flow restriction, not for a venturi.
But my "common sense" still doesn't "grok" it intuitively.
In any systems I somewhat understand, the aim is always to have gas/liquid flow to be smooth, not turbulent and compromised. (with the exception of golf balls and 'skin drag' systems)

Until reading this I thought the problem was that springers are lower margin/low volume products which are not built very high-tech and that hence nobody had bothered to try to integrate a venturi or valve.
If that's how they're supposed to work, I guess they are a compromise/"good enough" solution.

In a utopic world with no design constraints, would you then use a venturi and/or a valve between piston and barrel, or still not?

- Can you explain the part you wrote about that having some turbulence is actually good? I can't get my common sense around that. (I suspect it will have to do with blocking the flow as you said/acting as a valve)..

Hector Medina

6/9/2022 11:02:46

Arnoldus;

As far I understood from the Purdue Prof: the case where 600 fps were achieved, there was NO driving pressure, only the "pulling" vacuum, and this was also done by the Mythbusters, with more or less the same results.

I never saw an experiment where a C-D-N would be fitted on a "pull-vacuum only" version of the experiment from Purdue. That would also be an interesting challenge for the Purdue Prof.

The "quadrupling of power" you talk about is actually brought up by using TWO power sources (vacuum pump and compressor). Which is not too much to expect.

So, bottom line: the chain of experiments does NOT follow the scientific method of changing ONE thing at a time.
To ME, it's really hard to believe what the Prof is saying without some reasonable doubts.
Until I see a chain of experiments that follows the method and makes sense, I need to put this away as "pseudo-science".

AFAIK, there HAVE been previous experimenters that have tried "nozzled" TP's and AFAIK, they have not had much success.
Personally, I do not have the time to do it, but if you look into the literature, I believe you will find it.

When I said that SHORT TP's CAN work as a valve, I am referring ONLY to short TP's. Long transfer ports allow for air expansion and the sound barrier drops rather dramatically.

As per Wikipedia (https://en.wikipedia.org/wiki/Speed_of_sound) , the speed of sound with respect to temperature is given by:

C=331.5+(°C*0.606) in m/s

So, for example:
at 2,000 °F (1,093 °C), the sound barrier is at 993.6 m/s which translates into 3,260 fps.(Mach 2.9)

This means that the air CAN flow through the TP at very high speeds, as long as it is hot.
Once it expands on the pellet side, the reverse flow CANNOT flow back as fast. In THIS sense is where the TP's act like a "valve", but ONLY SHORT TP's. Long TP's allow the air to start expanding and cooling, and then the sound barrier drops in the FORWARD fase of the air flow.

My own experiments with shaped TP's in short TP guns as well as PCP's tell me this is correct.

So, NOT ALL TP's are valves, SOME TP"s MAY BE MADE TO ACT as valves. The long TP's of breakbarrels are NOT within this category.
There are OTHER ways, but that is research that is ongoing and I cannot disclose more.

What you call skin drag systems is pretty much why a turbulent flow that forms a "skin" around the sharp edges will always be more efficient than creating a full laminar flow that would need, not a nozzle, but an aerospike, because you have a VARIABLE pressure on the exhaust side.
I would recommend you read on aerospikes.

Springers arre built to a budget, yes, and the MAIN problem is that the first design was so successful that we have not changed it much over almost 150 years.
There have been springers built with "customizable" TP's, but most experiments have concluded that it is not worth the cost or the effort, mainly because any pellet change would "shift" the system out of the optimum operational point.

BUT, springers are incredibly high tech when you really want to understand what is happening inside and the difference in architecture that the length of the TP introduces is so great as to have to think of each style as a different kind of gun altogether.

As we move forward in technology, and assuming we are still shooting springers some years into the future I would still keep the "square but burr-less" TP in break barrels, except for the case of CDG's (controlled dieseling guns). Where there are other things that open up several interesting research avenues.

The "good turbulence" part comes, as you had already surmised, from the skin effect of flows.
AND from the need to adjust shape as the characteristics of the air flow change, which means that the curve that would be good at the beginning of the shot cycle, would not be appropriate at the end.
In the C-D-N world, the solution is an aerospike, in the airgun world the solution is a short TP.

Still, we love our break barrels, and so, we need to make the best of them.

;-)

It's a labour of love.

Keep well and shoot straight!

HM

Peter link

6/9/2022 17:38:02

What drives a projectile down a barrel is average pressure differential across the projectile. In a vacuum cannon, the differential across the projectile is one atmosphere (max). The vacuum in front is not pulling the ping pong ball; the atmosphere behind it is pushing it - just look at the direction the foil membranes bulge, before and during firing.

The air in the long barrel weighs a lot compared to the ball. So removing that from the front of the ball removes accelerating the mass of that air from the equation. So the air behind only has to work on the ball.

This guy demonstrates a number of vacuum cannon designs, including a "rapid fire" version: https://www.youtube.com/results?search_query=knighthawk+vacuum+cannon

Hector Medina

6/9/2022 20:17:02

Yes, Peter, I know that.

Reason why I wrote the actions between quotes.

;-)

HM

Peter

6/9/2022 20:20:26

Hector,

When one writes on a public forum, it is often the public that is being addressed, rather than the person that seemed to provoke the comment :)

Hector Medina

2012 US National WFTF Spring Piston Champion
2012 WFTF Spring Piston Grand Prix Winner
2013 World's WFTF Spring Piston 7th place
2014 Texas State WFTF Piston Champion
2014 World's WFTF Spring Piston 5th place.
2015 Maine State Champion WFTF Piston
2015 Massachusetts State Champion WFTF Piston
2015 New York State Champion WFTF Piston
2015 US National WFTF Piston 2nd Place
2016 Canadian WFTF Piston Champion
2016 Pyramyd Air Cup WFTF Piston 1st Place
2017 US Nationals Open Piston 3rd Place
2018 WFTC's Member of Team USA Champion Springers
2018 WFTC's 4th place Veteran Springer
2020 Puerto Rico GP Piston First Place
2020 NC State Championships 1st Place Piston
2022 Maryland State Champion WFTF
2022 WFTC's Italy Member of TEAM USA 2nd place Springers
2022 WFTC's Italy
2nd Place Veteran Springers

Hector's Airgun Blog

"Blue-Printing" a Walther LGV ©

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