Hello all,
I'm located in south Texas near San Antonio. I've been shooting for about 15 years, got into gas guns in the last 4 years, assembled a few AR-15s of various shapes and sizes (and shot them), and just assembled my first large frame AR. I've had some cycling issues with it and reading up on this forum has been very informative and interesting, so I thought I'd join up and answer the waterboarding thread here.
1) I do not have the Armalite recoil system
2) Buffer weights: 4.6, 5.4 oz
3) Buffer length: 3.25"
4) Buffer tube internal depth: 7 5/8"
5) Springs: Sprinco red, LMT 308
6) Gas system length: rifle
7) Gas tube length: 15 1/8"
8) Photo into magwell:
9) Photo of bolt face:
10) BCG clearance:
11) Gas journal diameter: 0.750"
Gas port diameter: 0.073" (nearest I can measure with calipers, a 5/64" drill bit will not fit)
12) Malfunction: Issues cycling with 146gr M80. Hotter 168gr .308 works fine. M80 works fine with a suppressor.
The upper is a Larure 18" Stealth 7.62 ultimate upper and the lower is an LMT MARS-H. I initially tried shooting the M80 with an Odin Works adjustable gas block and the LMT 308 spring with H3 buffer, and I either got no feeding at all, or jams. I diagnosed the gas system (block alignment, leaks, carrier/tube interface, gas rings) and am left with the conclusion that it's just undergassed.
The LMT spring is longer but with a lower spring rate than the Sprinco red, but the tension in battery is definitely higher. I switched back to the Larue fixed gas block and the Sprinco red/H2 that comes with the upper kit, and now it seems to feed M80 decently, with case ejection at 4:30 - 5:00, but won't lock back on an empty mag. With a suppressor on it cycles and locks back reliably, with case ejection at 3:00. Any weaker spring I could try than the Sprinco red, or would it not store sufficient energy to feed a round and go into battery? I also have an Armalite EA1095 which I haven't tried, but it seems stiffer and higher tension in battery than either the Sprinco or the LMT.
Thanks for reading and nice to be here.