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Hey all,
I'm curious about people's expectations for 300 Blackout AR pistols and cycling various rounds of different weights...
Here's the basic history:
Built my own lower (functions great, no issues)
Bought a fully assembled 300 Blackout upper with a 10.5" barrel and carbine length gas system.
(Side note: Me and 3 friends all bought the same uppers and built lowers)
At my house, we tried all 4 uppers and got these results:
It was suggested that they should have probably been pistol length gas systems, so we waited quite a while for the 10.5" uppers with pistol length systems to come in stock.
Waited a long time (though they kept me updated and communicated status well). Eventually, is seems like they weren't going to come in stock any time soon, so they suggested a 7.5" barreled upper with a pistol length gas system. I did quite a bit of research, and it seemed that, on average, due to typical 300 AAC powder burn rate, you'd lost maybe 200 FPS on the super sonic rounds and only about 50-60 FPS on the subsonic rounds, so I decide to give that a try. Here's the results from the next round of testing with this new option (only tested with one upper so far, instead of shipping all of them back and forth):
Thoughts and/or suggestions?
I'm curious about people's expectations for 300 Blackout AR pistols and cycling various rounds of different weights...
Here's the basic history:
Built my own lower (functions great, no issues)
Bought a fully assembled 300 Blackout upper with a 10.5" barrel and carbine length gas system.
(Side note: Me and 3 friends all bought the same uppers and built lowers)
At my house, we tried all 4 uppers and got these results:
- 150 grain: 3 of 4 uppers would cycle properly (the 4th cycled most of the time); short stroking
- 220 grain (subsonic): 4 of 4 wouldn't cycle properly
It was suggested that they should have probably been pistol length gas systems, so we waited quite a while for the 10.5" uppers with pistol length systems to come in stock.
Waited a long time (though they kept me updated and communicated status well). Eventually, is seems like they weren't going to come in stock any time soon, so they suggested a 7.5" barreled upper with a pistol length gas system. I did quite a bit of research, and it seemed that, on average, due to typical 300 AAC powder burn rate, you'd lost maybe 200 FPS on the super sonic rounds and only about 50-60 FPS on the subsonic rounds, so I decide to give that a try. Here's the results from the next round of testing with this new option (only tested with one upper so far, instead of shipping all of them back and forth):
- 125 grain: Cycled fine (with or without suppressor)
- 150 grain: Cycled fine (with or without suppressor)
- 208 grain (subsonic): Wouldn't cycle at all (still short stroking, suppressor or not)
- 220 grain (subsonic): Cycled fine with suppressor, but still short-stroked without it
Thoughts and/or suggestions?