We've got two 6.8's in the house and both have been doing the same thing. I didn't notice the first one doing it until I built the second one and was doing a more thorough function check on it. So here's what going on. Both rifles lock back on an empty magazine but, they lock on the carrier and mag catch. Not the bolt and mag catch. I'm clocking 95gr projectiles at over 2800fps.
Carbine buffer and carbine springs. Mid length gas system. I even took a deer last year with one of them and it doesn't suffer any apparent losses in accuracy.
So here's what I've tried so far:
Lubed buffer spring and buffer extension
Checked gas rings
Checked gas block alignment
Ported gas tube to match diameter of gas block.
Checked gas port in barrel.
Sealed the gas tube to the block and gas block to the barrel with gasket sealer.
Changed buffer weight down to 2.2oz
Swapped bolt carrier from a known working firearm
None of that made a difference.
So I took one of the 6.8 uppers and put it on my 300blk lower. The same firearm that was the donor bolt carrier for test. I even left the carbine buffer in it. BANG. Lock on bolt!
OK so WhAT is your major malfuction???
I'm out of ideas and internet searches aren't giving me any insight. The only thing I can think of now to try is, turning the buffer tube back out a turn or two.
Anyone got any ideas?
EDIT: I just went to back out the buffer extension by one turn and the buffer retainer was free to come out. So that's not going to work either.
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