i recently picked up a used 5.45 upper. when i first got it, it had the A2 FSB and we swapped it to a 4 rail gas block. at the range, the gun would not cycle at all, it would fire the round but there wasnt enough force to push the bolt back. after playing with it for a while, we managed to get it to push the bolt about half way back but thats all.
we then took it back home and cleaned it and replaced the gas block with a MI railed gas block. took it to the range again yesterday and it will now eject the round completely but it wont chamber the next round. the bolt cycles but its not grabbing the next round.
my research has led me to believe that it is short stroking? one guy at the range suggested that i try a lighter buffer or a PRI fatboy gas tube. i am running this upper on a LMT lower with a 2 stage trigger, car buffer and spring with a ACE socom stock.
A fat gas tube is exactly the wrong answer.
Replacing the gas block with the original is the right answer.
A common problem with short-stroking following gas block replacement is misalignment of the gas port and the port in the gas block.
The taper pinned GB is much easier to realign since it has pins that put it back in the proper position.
You have classic short stroking. I’d recommend replacing the gas block (which is probably aluminum) back to the original FSB and see if it starts working again. You may have it out of alignment but surely it should work with the FSB.
There is, but for now, their suggestion is to swap back to help diagnose the problem. Once you know for sure that the gas block is the culprit, you can take a closer look at why it may be a problem.
