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Replica Tihar (Metro Pneumatic Rifle) Possible?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Replica Tihar (Metro Pneumatic Rifle) Possible?

Unread postAuthor: cowscankill » Tue Jun 21, 2016 12:28 pm

Hello hello, back from the dead for another year. Some background for ya:
It seems I can't escape spudding no matter how much time passes. I made a new friend last semester who is really into cosplay and video games. He's pretty awesome at making stuff:
He likes post apocalyptic builds like Fallout and Mad Max, and really liked the game Metro. With us both being builders, he has convinced me that I should build the Tihar which is a pneumatic rifle from Metro:

I've looked at this thing many times before, but after my last build going semi-automatic, I feel pretty comfortable taking this on again. First, I can give you the basics that I understand, skip this is you just wanna see the design problem:

Pressure: 0-12 (whatever that means, assuming bar means ~0-175 psi)
Ammo: 15mm (.59" or .59 cal) steel bearings
Capacity: 15 shots, and pressure drops by 3 (assuming bar, 43.5 psi drop per magazine)
Operation: Semi automatic
Reload Procedure:
1) close bottle valve to the pump (not sure why)
2) rotate 'bolt arm' down (rotates whole assembly, hard to explain but here at 1:05
3) pull mag forward and out
4) load new mag forward then back (think of batteries in a TV remote)
5) rotate 'bolt arm' up
6) open bottle valve to pump (again not sure why)
Best I can approximate, the chamber is about 6" x 2.3"dia if the whole gun is ~46".

Now, I don't mind doing 'inspired' builds where I make a gun that looks like what it's supposed to look like. But I don't see the fun in building this thing as a 300psi metal coax when I could give it a semi auto tube magazine feed. Coax seems too easy and simple at this point. So here's my problem:

What the heck kind of mechanism can I fit in such a tight space? The ammo loads into the back of the body, air is also injected into the back about an inch behind that, so where does the trigger go? From how jammed everything is the larger cylinder that makes up the main body seems to be more of a sleeve to hide parts, so I'm willing to jam whatever works in there. The space looks too small for one of these QEV especially since it usually has a secondary reservoir attached to it.

Best I've been able to come up with at the moment is to use a hammer valve but I'm wondering if a burst from a hammer valve will have enough power to launch a 1/2" steel bearing at less than 300psi? This would fit for sure, but not sure how to attach a mag with it in such limited space:
The body looks about the size of 1.25" PVC's OD, which I'll probably use as housing.

I've got two weeks to plan and maybe a week of build time if I wanna have this thing actually get built. Any help appreciated.

EDIT: Edited some sizings. Plan on reversing the feed direction so the bearings are pushed forward instead of backwards, to help fit everything.

EDIT 2: Another possibility will be to build something Dragunov-y with a Metro apocalypse style (onboard pump and tube magazine). The Tihar design basically has an S of steel as it's frame, and if you're putting a lot of force on the pump I see that metal flexing. And since I don't have a welder, this looks like a bad idea to make from plastic...hummm
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"Make everything as simple as possible, but not simpler." - Albert Einstein
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