300BLK Subs at 9,300ft

[belizejet]

Elevation is a factory with speed of sound though. I want them to stay sub sonic.

[belizejet]

I've chronoed, used NiB BCG's, reduced recoil spring, etc. They are subsonic and loaded pretty much to max without breaking the sound barrier. Even with a can, that should provide more back pressure, I'm surprised I can't get it to run. It ejects the brass but doesn't quite come back far enough to pick up another cartridge. I could load it slightly hotter and see what happens. If it starts breaking the sound barrier then I've got to go after the gas system. I agree with Tim and Mark. It's probably a gas issue. I'm pretty much dedicating this 8.5" upper to subs anyway so maybe I should put a standard block on it and enlarge the port slightly. I've heard it's real easy to make it too big though. May be calling you Tim.

[brutal]

Could you be overgassed? Too much chamber pressure with the can installed and the round is slow to eject.

My Sig716P would not cycle (full power ammo mind you) suppressed. The hotter they were, the worse it ran. The replacement model has been running well, but I'm not convinced the accuracy is as good.

[Tim K]

I was just wondering the same thing. I'll bet he tried turning the gas down already, though.

I have a spare 8" barrel you can try if you want. The gas port is 0.125". I guarantee you'll have to turn the gas down...

[belizejet]

Yes, I started with the gas low. I've literally shot like 100 test loads through this thing with different configurations of all kinds. It's getting expensive now.

[SAnd]

I assume the bolt will lock back with the bolt catch manually. That proves that you probably have enough bolt travel.

Try another upper on the 300 lower. And try the 300 upper on another lower if you can.

Good Luck.

[AKA-Spook]

#31 drill for the gas port, and I've heard of reducing the buffer's weight to assist cycling.

[Tim K]

Come get mine and swap uppers and lowers around till you figure out the problem.

[belizejet]

Tim, is yours an 8.5" also? I've tried different lowers. I'll get in touch soon. I'm working on the East coast now.

[275RLTW]

Watch it be something cometely unrelated like wrong rear sight aperture...