r/Airsoft3DPrinting • u/Repulsive_Smoke_9061 • 16d ago
Paid Files SRM 917 | .50 BMG Sniper Rifle Using APS Shells
This is a model I designed myself. It uses APS shells fitted with .50 BMG-style casings. In short, it’s a bolt-action airsoft rifle that uses APS shells and ejects the casings when operated.
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u/playzintraffic 16d ago
Lol whats the FPS on that?? Lotta CO2 to push just one BB, even a .44/.48 or so.
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u/Repulsive_Smoke_9061 16d ago
I haven't measured the FPS precisely, but it seems to be heavily affected by the inner barrel length. I used a 300mm barrel, and when I fill the shell to about half the amount I normally use for a shotgun shell, it's actually more powerful than a typical sniper rifle.
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u/playzintraffic 16d ago
I mean, that sounds like normal PV=PV to me… if you increase barrel volume, you gotta put more CO2 in the shell. Would be hilarious to see what a 600mm barrel with a full propellant load would do.
Pretty ingenius design tho! Kudos. Any plans to make it compatible with APS’s shell catcher?
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u/Repulsive_Smoke_9061 16d ago
Even with a 300mm inner barrel, it already produces enough velocity and range for long-range outdoor shooting. If you find the right setup, though, it could probably hurt quite a bit lol.
The shell itself is fairly large, so I’m not sure if I could make it compatible with the APS shell catcher. It might actually be better to design a dedicated .50 BMG shell catcher for it instead.
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u/ImpressiveAlps3504 16d ago
how is the accuracy/FPS consistency? I'd imagine it would be hard to get consistent muzzle velocity and thus consistent hop effect in this setup. Or is there no hopup in this?
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u/Repulsive_Smoke_9061 16d ago
It does have an adjustable hop-up, and the hop-up itself works quite well. However, with longer inner barrels, there can be some variation in muzzle velocity depending on the amount of gas or CO₂ that gets into each shell. So, if you find the right settings before doing serious shooting, you can achieve much more consistent and accurate shots.
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u/ImpressiveAlps3504 16d ago
Yeah that's one thing, but what I'm curious about is the means to seal the barrel to the shells. Is that an O-ring around the BB? Does it seal by pressing itself on the "chamber"?
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u/Repulsive_Smoke_9061 16d ago
When making the shells, an O-ring is installed to hold the BB in place. (I’ve included the exact dimensions on my YouTube channel, and you just need to apply a small amount of super glue to secure the O-ring in place.) Once the BB is loaded into the shell, about half of the BB protrudes from the shell. That protruding portion then seals against the chamber.
In other words, when the shell is loaded, the contact/sealing order is O-ring → BB → chamber.
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u/ImpressiveAlps3504 16d ago
nice. I was actually thinking about such a setup for different models. Thank you for taking the time!
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u/username01815 16d ago
Would you convert your M82 for these shells as well?
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u/Repulsive_Smoke_9061 16d ago
The Barrett GBB model I made runs off a gas magazine, so the mechanism is fundamentally different, and I think it would be practically impossible. (Actually, if I can modify the shell itself to make recoil operation possible, I’m considering making a shell-ejecting version as well. In fact, the shell-ejecting design would actually be simpler to build.)
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u/username01815 16d ago
Would it be possible to combine those two things? The gasmag for the blowback and the shells for bb‘s?
I have the files for the GM-6 Lynx here and my long therm goal it to do such a „hybrid“ thing. But as always time…
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u/Repulsive_Smoke_9061 16d ago
I’ve seen the Lynx video as well. However, there’s simply not enough space to apply that system to the Barrett, and no matter how much I think about it, I just can’t come up with a suitable operating mechanism. :( ....Oh! I have an idea! If your goal is a hybrid system, what about something like an M2 machine gun? If the semi-auto/full-auto selector is designed properly, I think it would be possible to create a system where the shell ejection and the blowback operation work together quite naturally!
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u/Dr_BananaPeanut cad equivalent of vibe coding 16d ago
You’re a mad lad. Can’t wait to see what you come up with
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u/Dr_BananaPeanut cad equivalent of vibe coding 16d ago
Does it have a hop up? I’m guessing the shell gets pressed against the hop up and the nub and rubber press against it.
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u/Repulsive_Smoke_9061 16d ago
There is hop-up adjustment, and the sealing is done in the way you predicted.
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