Precision rifle alternating between double feeds and short stroking-Troubleshoot how?
I have an upper (sitting on a Gen2 Chainsaw lower I built) that has been giving me fits - short stroking across every buffer combination I've tried, but throwing double feeds almost as frequently. I've only had limited range time, and only taken it out four times, totalling less than 200 rounds through this thing, but I can't find a buffer combination that can make the short stroking and failure to lock back really go away, nor can I get through a dozen rounds without some sort of failure to feed.
So far I've tried: H2 Buffer, Springco Blue Spring; H Buffer/Sprinco Blue; CAR Buffer Sprinco Blue; H-2/stock spring, CAR/Stock Spring; A5H2, A5H3 with stock VLTOR spring on the buffer/spring front. Still getting failures to lock back even with the CAR/Stock buffer/spring setup running IMI and PPU M193, and still getting double feeds in magazines which have ran otherwise faultlessly.
Only other part of note is that sometimes the BCG feels a bit stick while unlocking - at first I assumed this was a breaking in process, as this is a match barrel, but it's persisted, and is somewhat inconsistent. I later noticed that the extractor pin at some point had protruded out a bit, but seems to have been sheared or pressed back enough that it doesn't seem to interfere - still no issues with ejections (makes very nice neat piles... when it decides to run in semi). Subbed in a different BCG, got a couple short strokes and gave up on that idea.
I'm inclined to think maybe gas tube, or tolerance stack with that pin dragging slightly and the tight chamber as well as bolt lug friction, but outside of visual inspection there's not a ton I can do to look at that. The double feed also seems perplexing - this lower feeds other uppers just fine using the same magazines, though a fraction of these are probably just me reflexing a tap rack bang when I get a soft trigger because the bolt is caught halfway on the way back.
What I'm at a loss for is if there's any more user end troubleshooting I should really look at, or should I just stop wasting time and ammunition and most likely send the complete upper back to where I ordered it from? Everything I've tried points towards that, though I may not have the round count to really say that the lower itself is GTG, I've just never had to troubleshoot two simultaneous malfunctions for which I don't know of a common cause outside of crap grade rifles, and this hardly meets that description.
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