B.A.R. Pnuschnikov full auto prototype

[jackssmirkingrevenge]

All this was pioneered by Al-xg so I won't take any credit for it.

Really it was the FX Revolution/Monsoon series that pioneered the design in the pneumatics field, though that doesn't at all detract from al-xg's achievement

I'm seriously tempted to give it a go with cartridges along these lines, using compressor pressures and a 3/4" bore.

So many ideas, so little time

[Brian the brain]

The coax version of it, well yes..
Cartridges came to mind as well as pellets..but I'll try and finish what I got now first.

At first I wanted to have the spring inside of the outer casing..with only a rod coming out..but the dimensions of the stuff I had to work with would not allow it.
Lathe time!

Oh..just wanted to add I will also put a cover over the snapvalve ( it is: the ventholes are closed off by the piston in resting position)
This cover will have a small venthole so it will muffle the sound. I have done this before with great succes.upscaling the gasram will help to muffle the muzzleblast..
If I can I will make it so you will only hear it rattle and hum..

I'm also contemplating the use of a ballbearing and a stepped sleeve as the breechlock, if sheer springpower won't suffice.
Also I intend to put a shield over the breech area to keep the action away from my cheek..as this is a problem in bullpup design.

Damn this thing is becoming so cool.
I hope more people will be inspired to try forced blowback.

[POLAND_SPUD]

It's taking advantage of that last bit of air wich would normally be mostly wasted

well I don't want to argue but most likely the bolt can't move much during that 6 - 8 ms that it takes for ammo to travel down the barrel...

so I suppose that the performance loss will be negligible (meaning you might not even be able to notice it or measure)

I just feel it makes things more complicated than they have to be - you need to join the airram with the bolt with some sort of a rod (and that means extra friction, more exposed parts etc.)

[al-xg]

So on your design the bolt is acting directly on the bolt, just helping to overcome friction or inertia ?
What stops the bolt from recoiling in the first place ?

On the version I built the ram only needed to unlock the bolt, even though the pressure only acts on the freed bolt for a very short time the relatively high pressure on the lightweight bolt gives it a high acceleration.

Haven't been able to touch anything remotely pneumatic since the competition and I probably won't get the opportunity until some time in June.
Frustrating

[Brian the brain]

What stops the bolt from recoiling in the first place ?

Right now; nothing.There is no bolt yet.

I'm also contemplating the use of a ballbearing and a stepped sleeve as the breechlock, if sheer springpower won't suffice.

Most likely, I will need to put a lock on it like I mentioned.
A stepped sleeve and a ballbearing.
The ram wil aid both in recocking and unlocking

It can be done in a single move.
I'm hoping to get less of a blast coming from the breech that way, but frankly, I will be tuning and tinkering a lot to get it to work and I'll be happy if it reloads at all.
The lock does offer the benefit of using a very light spring for the bolt.

I just feel it makes things more complicated than they have to be

That's kind of the point.
I want to try something new. Once I have perfected it I can show people how to do it in the most simple way.
Your boltmechanism requires a 3 way valve , a specially machined block and a pneumatic cilinder.
This idea is not more complicated than that, just a different challenge.
I loved the technical challenge on Old Shat where I had to move the hammer on the outside while the trigger was inside and the whole hammer valve repeater idea.
This was not neccesary either.I could have piloted it with a blowgun.
It's still all basic pneumatics.

[POLAND_SPUD]

Your boltmechanism requires a 3 way valve , a specially machined block and a pneumatic cylinder.

naaah you didn't understand me....

I don't want to convince you to use the design I used (3way valve + air cylinder) but just to modify your design (blowback)

Basically it all comes down to whether you really need that airram where it is now. As al-xg has pointed out pressure will be acting on the bolt too
so you it possible that you might as well not need that airram at all

EDIT
I modelled in fluidsim how far the bolt would retract by the time the projectile leaves the barrel...
I simply attached an air source (300 psi) to a single acting air cylinder (11mm diam piston X 50mm stroke)... the programme calculates the mass of the cylinder on its own but I added 80g to it and I used a slightly stronger spring (20N)


and it seems that in the first 12ms after the valve opens the bolt would move only about 20mm... of course you can get better results with a stronger spring, heavier bolt and more friction...

it might require some tinkering to get it too work right but that's something you have to do anyway with the setup you use right now

[Brian the brain]

I do understand you.
All of it is a bit unneccesary.
And yes, moving parts are dangerous if not carefully handled.

I just wanted to point out every system has it's pros and cons.
If there would be no cons the topic wouldn't be any fun anyway..

I just want to get this done and then improve on it.
Have you taken a look at AL-xg's protoype?
His ram is pretty far forward and it has exposed moving parts.

But the idea the ram would only have to be used to unlock the bolt does seem more convincing now.
I thought it would need a bit more umpfh to get it to load a projectile, since all pressure escapes as the breech opens up.
We'll see...

Basically it all ocmes down to whether you really need that airram where it is now. As al-xg has pointed out pressure will be acting on the bolt too

so you might as well not need that airram at all

I've been wrong before..but for now I believe I can get it to work.
I'll try your suggestion if needed.


Pure blowback is hard to get right and will go at the expense of performance ( a little bit at least)

The main reason ofcourse to go for this ramdriven recocker is the "rule of cool" ( yes I embraced that stuff pretty fast!)

If all fails atleast I got a step closer to beating JSR at his failing prototype game...

[al-xg]

The air ram makes delayed blowback possible, as BTB said it means you can have a very light bolt spring but still have it move back at the last minute (millisecond ) and requiring less energy.

At first I had intended to get the air ram to help push the bolt back after unlocking it. With no bolt lock and no projectile to seal off the barrel the bolt
still fully cycles. Depending on the air ram position down the barrel it also cycles with the bolt lock on a dry fire.

[Brian the brain]

At first I had intended to get the air ram to help push the bolt back after unlocking it

Just like me, but I guess all it has to do is unlock it huh?
That makes life easier.

[al-xg]

Well I guess it would still help, and the air ram port could be placed further forward. The piston stroke would have to be a bit longer and a lighter spring might be needed although it looks OK in the video. The spring just needs to be fast enough to return the ram into position in time. (I found even an elastic band was fine, although really ghetto)
The main reason I didn't in the end was actually that I decided to have the pump action grip to manually cycle the bolt and the bolt would have needed a pin on both sides.

But yeah just unlocking should work fine provided the bolt and bolt spring are light enough.

Exterior moving parts are really only an issue in the bulpup configuration, but they can quite easily be covered up anyway. It does look really cool though.

[Brian the brain]

New vid:

[youtube][/youtube]

DAKKA DAKKA dobre da?

[Demon]

The sound that it makes is so cool !

!!! Ratatatata !!!

You dont stop being awesome

[al-xg]

It does look really cool though.

[Brian the brain]

The sound that it makes is so cool !

It does look really cool though.

Never doubt me again.. 8)

It will sound a lot cooler with the action working..
More kaklunk!
Plus it will look a hell of a lot cooler when it starts spraying ballbearings!

[Demon]

Plus it will look a hell of a lot cooler when it starts spraying ballbearings!

What fps do you expect with you 11 mm bb's?

And where can you put a magasine on that?