Breech System For historical Pak 36

Harness the power of precision mixtures of pressurized flammable vapor. Safety first! These are advanced potato guns - not for the beginner.
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Alexypak36
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Wed Feb 03, 2021 5:01 pm

Hi everyone
I introduce myself. My name is Alexy, I come from France. I am a student in an engineering school and passionate about history of the WWII.

I have a project that has been going on for several years :
make the most realistic German WWII Pak 36.

To do this, I made CAD to make a breech loading system. I know the question has already been asked but no one is part of the idea of ​​making the whole system in a shell.

I ask all the English-speaking community to help me to realize my dream ^^. I started with a standard system with a burst disc and a mixture of air and MAPP.

I will put a diagram so that it is more meaningful for everyone.
2021-02-03_225700.png
Obviously this project is purely for historical purposes.
excuse me for my english level. French people suck in English ^^.

Have a nice day!
Alexy.
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Fri Feb 05, 2021 7:54 pm

Are you injecting fuel and air that's already been mixed? If so, that means you have to store the mixed gas in a separate container which is very risky. A static electric spark could cause the container to explode. It's better to add the fuel first and then add air separately. This way, the fuel stays in a fuel container and the air just gets pumped in.
Other than that, it looks like it should work great so long as you can add fuel through the schrader valve. Do you have a sketch of the rest of the gun?
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Alexypak36
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Sat Feb 06, 2021 7:43 am

I will use the same principle as in this video. mixing takes place directly inside the combustion chamber.



Step 1 :
I put the gas
2nd step :
compressed air

for the rest yes I have the rest I am finishing the design.

The .22 blank firing would be enough to ignite the mixture? and how to guarantee
sealing with the burst disc? a seal is enough?
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Rumpler
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Sat Feb 06, 2021 11:45 am

I used to fill my first hybrid by injecting the fuel into the bicycle pump (suction hole on top) with a big syringe while drawing the handle up, and continued to fill plain air to the desired pressure.

You'll need to seal that .22 if there is any pressure in the shell.
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Sun Feb 07, 2021 7:27 am

Bienvenu!
Alexypak36 wrote:
Wed Feb 03, 2021 5:01 pm
excuse me for my english level. French people suck in English
Pas autant que les anglophones qui essaient de parler français ;)

Ah, hybrid cartridges... if you fancy a bid of reading, maybe this extensive thread will be of interest: viewtopic.php?f=28&t=19504
The .22 blank firing would be enough to ignite the mixture?


It should be, but you also need to make sure the blank does not leak pop out under pressure as Rumpler pointed out.

It seems to be that using a percussion based system is unnecessarily complicated compared to an electric one. I assume you chose it because you wank to replicate the Pak mechanism?
and how to guarantee sealing with the burst disc? a seal is enough?
An o-ring squeezed between the burst disk and the thread face would suffice, this is the system I used in all my burst disk hybrids:

Image
I will use the same principle as in this video. mixing takes place directly inside the combustion chamber.
I would suggest that for a 37mm sized cartridge, injecting the fuel with a syringe would be more practical.

Fuel metering with a syringe
Last edited by jackssmirkingrevenge on Sun Feb 07, 2021 1:08 pm, edited 1 time in total.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Alexypak36
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Sun Feb 07, 2021 11:15 am

Yes in addition to being realistic, the percussion system is reliable. I don't trust electricity ^^.

On the other hand, the loading of gas by syringe is not stupid! on the other hand, it is necessary to create another hole to fill the combustion chamber or to use the Shrader valve is possible?

because I have a total diameter of 46 cm (18 inch). I try to have the most compact and simplest system.

after efficiency levels I have no idea, however, I used the HGDT simulation software.
I wanted to know how to calculate precisely the mixture. park eque on the video I see 1 psi of MAPP gas and 13 psi for air for example.
how to guarantee the precision of the value of 1 Psi (manometer) I think it is insufficient.

But thank you for your feedback I will start the machining phase to do my first tests while waiting for me to finish the Pak 36
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Sun Feb 07, 2021 2:21 pm

Alexypak36 wrote:
Sun Feb 07, 2021 11:15 am
Yes in addition to being realistic, the percussion system is reliable. I don't trust electricity ^^.
Electric ignition is pretty reliable. Even the Germans thought so during WW2, most tank guns like the Kwk 36, 40 and 42 had an electric primer.

Also anyone who's ever shot a rimfire will tell you that .22 ammunition doesn't always go bang either!

Personally, I would make the percussion mechanism close to the real thing, but use it to make an electric contact instead.
On the other hand, the loading of gas by syringe is not stupid! on the other hand, it is necessary to create another hole to fill the combustion chamber or to use the Shrader valve is possible?
No, you can inject it directly into the mouth of the cartridge before you put the burst disk. It sounds counterintuitive, but unless you actively try to blow it out, the gas will take an extremely long time to diffuse into the atmosphere.
after efficiency levels I have no idea, however, I used the HGDT simulation software.
I wanted to know how to calculate precisely the mixture. park eque on the video I see 1 psi of MAPP gas and 13 psi for air for example.
how to guarantee the precision of the value of 1 Psi (manometer) I think it is insufficient.
That's the beauty of syringe fueling, no need for a very precise pressure gauge like you would with manometric fueling.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Alexypak36
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Mon Feb 08, 2021 3:59 pm

let us admit that I use the principle of filling with the syringe how to calculate the quantity to be injected into the chamber as well as the compressed air and how to calculate the ratio?

can we determine the force that the gun will have on the projectile, ie how many newtons will have to resist the projectile during the explosion?

it is to have an idea of ​​the design of my projectile ^^
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Alexypak36
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Tue Feb 09, 2021 5:14 am

At this stage of the design, I have almost finished the 3D design, I still have a little work to do for the mechanism, but otherwise it's almost finished ^^ 8-)
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Tue Feb 09, 2021 6:30 am

Alexypak36 wrote:
Mon Feb 08, 2021 3:59 pm
let us admit that I use the principle of filling with the syringe how to calculate the quantity to be injected into the chamber as well as the compressed air and how to calculate the ratio?
I like how you directly translated "admettons que..." :)

I explained the calculations in detail here: viewtopic.php?f=27&t=22301

Let me know if you want me to clarify, même en français si c'est plus compréhensible.
can we determine the force that the gun will have on the projectile, ie how many newtons will have to resist the projectile during the explosion?

it is to have an idea of ​​the design of my projectile ^^
HGDT can tell you the pressures and accelerations involved.

I am guessing your barrel is going to be a smoothbore, so what do you plan on doing to stabilize the projectiles?
Alexypak36 wrote:
Tue Feb 09, 2021 5:14 am
At this stage of the design, I have almost finished the 3D design, I still have a little work to do for the mechanism, but otherwise it's almost finished ^^ 8-)
Looking good! Soon all you will need is some light Soviet tanks :D

hectmarr wrote:You have to make many weapons, because this field is long and short life
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Tue Feb 09, 2021 7:02 am

AMAZING VIDEO !!! Poor soviet T26.... ^^

I will do the calculs at the evening, I will see if it is good. I send to you the resuslt to have a second check with people more competent than me :D
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Tue Feb 09, 2021 9:48 am

good, now we have to draw rounds and make them whistle while passing !! xD

in real life I'm sure it's possible to do it ^^
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Tue Feb 09, 2021 9:58 am

Alexypak36 wrote:
Tue Feb 09, 2021 9:48 am
good, now we have to draw rounds and make them whistle while passing !! xD
There are some Nerf projectiles that incorporate a whistle:

Image

Honestly though, with a larger bore hybrid, a projectile is going to make plenty of noise anyway without having to induce it artificially ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Alexypak36
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Tue Feb 09, 2021 10:25 am

and make tracing rounds ! i thinks is not necessary. it's too complicated for a good results. I thought of vortex nerf rocket. I seem afraid of losing performance.
you have already tried to make rounds spinning inside the barrel with a smooth barrel like maybe .12 brenneke shell into a shotgun
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Tue Feb 09, 2021 10:53 am

Careful with tracers!

You could probably take some material from a signal flare or a party "sparkler" and put it in the base of your projectile...
you have already tried to make rounds spinning inside the barrel with a smooth barrel like maybe .12 brenneke shell into a shotgun
Image

Contrary to popular belief, the "rifling" on this type of slug does not actually induce any spin in the barrel or in the air. Rather the slug remains stable on account of it having a lighter polymer or felt "tail" that induces drag when the slug attempts to tumble.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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