I’m working on tuning a 300 BLK with a 7.5” PSA upper.
I started with a PSA lower w/ LAW folder and an Aero 8” upper. Initially, with the original carbine spring and buffer, recoil was harsh, and it felt like the bolt was slamming back. When I went to an Aero Precision H3 buffer (5.6 oz) (plus the weight of the LAW adapter) and a Springco “extra power” (Red) buffer spring, it all worked well, ejecting to 3-4 o’clock and locking back on empty magazines with 110 gr TAC-TX, as well as 147 gr FMJ.
Then I ordered a Surefire SOCOM 762MINI2 for my 300 BLK
Then I found a deal on an Aero stripped lower, and build it up with some nice Geissele bits.
Then I got a deal on a 7.5” PSA upper, complete with BCG and CH.
So I decided to assemble 2 x 300 BLK pistols from my components.
-One optimized for supersonic 110 Barnes TAC-TX for backpack carry (mostly in vehicles)
-One optimized for suppressed subsonic Hornady 190-grain Sub-X for indoor use in home defense
Bonus points if the “optimized for suppressed” gun also was good (not harsh) with supersonic Barnes.
In testing today, it turns out that the 7.5 PSA upper (when mounted on the PSA lower w\LAW & red spring & H3) is undergassed (or more accurately, over-sprung). It would cycle 147 gr FMJ and 110 gr Barnes, but wouldn’t lock back on an empty mag. And it wouldn’t even cycle 125 gr FMJ.
So I’m thinking that the 7.5” PSA upper will be the supersonic upper, and the 8” Aero upper (with more gas) will be the subsonic upper.
I’m open to suggestions as to whether I lower the spring or the buffer weight (or both, but that involves changing two variables at once) on the lower to get the “less gassed” 7.5” PSA working correctly.
Then I’m open to suggestions for what to use for spring & buffer for running the 8” “more gassed” Aero upper subsonic suppressed. In my ideal world, it would be reliable w/ subsonic unsuppressed, optimized for subsonic suppressed, and functional w/ supersonic (but probably a bit harsh). I’m guessing I’d start with a basic carbine spring & buffer. It will have a LAW folder (and associated additional reciprocating mass), too.
If I have the selection of more vs less gas for the uppers messed up, and using them in opposite roles somehow makes more sense, please set me straight.
Mentions below because you might be interested ( @FPS), you commented on the 7.5” BCM vs 8” Aero thread, or I just wanted to get your input ( @Trigger, @rob_s).
Attn: @FPS, @Flamingo, @@Doc_Glock, @vaspance, @Clusterfrack, @Idunnmobile, @Cool Breeze, @Totem Polar, @Trigger @rob_s