
Originally Posted by
WS6
I just checked the problem upper on the known good lower that it jammed on with the H2/Milspec spring.
It seems to fit normally. The bolt-catch engages the bolt to the same depth as it does with the known good upper on this known good lower.
Now I am out of ideas, considering that it jammed on this lower, too, and the dimensional problem that I THOUGHT existed with the upper, is in-fact something funky with that Noveske lower. Yet it also jammed on a good, proven upper.
The H3 and Blue spring should not be required for a clean SBR to function with a lower backpressure can like a Surefire. There is something else going on, here, and I'm just masking it with an oversprung, overbuffered compensation.
I did speak with Surefire, and when they tested the upper, they had no function issues on their lowers. They ran it on their MK18 lower, IIRC.
At my wits end on this thing. Here are the facts so far:
-I only shoot the rifle suppressed, using a Surefire 556-212
-Factory built Noveske lower (FFL Gen 2)
-Factory built Noveske upper (VLTOR MUR/VIS Monolithic, 10.5" barrel)
-Happens with PMC XTAC M193
-Ejection is to the 1-2 O'clock and very brisk
-Sometimes happens when reloading and using the bolt-release.
-Happens using another lower which has never had issues on another upper
-H2 buffer, mil-spec spring (5-800 rounds old)
-Sometimes there are "near misses", when using the bolt release on a reload, I can feel it "release...hit...pause...chamber".
-It has done this with newish PMAG's which have been proven in other guns
-It has done this with Lancer L5 AWM which have been proven in other guns
-It was generously lubed with Froglube the first time I had the issues, and with FIREClean the second. Correct procedures.
-I does it free-standing as well as when resting the mag on the bench.
-I tried it with an H3 and Sprinco Blue spring. Ejection is still to the 2-230, but it appears that this combo overpowers the method of failure.
-Always locks back on empty
Yeah, it ran a mag or two over-buffered and over-sprung, but I want to know the real issue.
Any other ideas, anyone? I might buy over or under-gassed if it didn't also jam when I used the bolt-release. So the gas-system is out of the picture as the problem, IMO
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