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Posted: 8/31/2010 8:43:16 AM EDT
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Hello all, I have an SPR that I built. The problem is that its not cycling all the way or not at all. i think its under gassed. The gas block looks straight though.....?? I tried it out today and it wouldnt cycle with out the can on. When I put the can on, it started to cycle but it wouldnt always pick up the next round. What could be causing this?
Its an 18" pac nor barrel with rifle length gas system. Im running a carbine buffer in it. Could this be the problem or is the gas block still crooked?? Thanks, Ryan |
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Not enough gas getting back to the receiver ... sounds like the can is increasing the pressure but still not quite enough.
Either the gas block is not aligned with the gas port hole in the barrel or the hole is not large enough or there is something clogging the tube or gas block and it's restricting the flow of gas. |
the gas tube was brand new, the gas block was good because i took it off another build and it functioned fine on there. The barrel is used but in very good shape, about 200 rds down the pipe before i bought it. I would think that it has to do with the gas block being missaligned or the buffer or something. The gas block looks straight though.....so i dont know
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Your gas block could be on straight, but be a bit too far forward or aft.
One thing to check: generally you don't want the block up against the 'step down'/ridge between the gas block and the barrel leading to the chamber. Normally there is a bit of space reserved for the handguard cap. If your block is up against the stop and the hole is not much larger than the gas port you'll have issues with getting enough gas to operate. |
i think that it is up against the shoulder. I also had alot of problems getting the gas block on! Its a troy micro gas block. It was super tight when i tried to put it on the barrel. In fact i had to use a mallet and wooden dowel rod to get it on! Its not easy to move at all, if I want to move the gas block, i have to smack it around with the mallet and dowel rod 
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You can sand the inside of the gas block with some 600-800 grit sand paper and you finger (real easy) until it fits better .... don't sand the barrel.
I took and old round hand guard end cap and used a band saw to cut it in half ... then sanded the edges ... I use that as a spacer to index the gas block off the shoulder. |
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If it is indeed a Pac Nor barrel, I wouldn't go drilling on the gas port. Odds are that it's right and with the problems that you are describing, the gas port is the last thing I'd get to on a quality barrel. If the gas block is seated flush with the step (it's already been said), you probably aren't getting enough gas through the system.
If that doesn't do, it (considering how tight you say the block is, I'd check the bolt/carrier assembly for smooth operation. |
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Quoted:
I will have to try moving the gas block back a little. Yall dont think that the buffer would have anything to do with the problems? You mean forward ... towards the muzzle .. should be about 1/32" off the shoulder. I seriously doubt the buffer is the culprit here ... I have run carbine buffers on rifle and mid-length gas systems before without any issues. You do have the "whole" setup ... carbine tube, spring and buffer right? |
Thank you to all who replied and helped!! After I tore the upper apart, I knocked the gas block out a little more and took it to the range. Much to my supprise it worked I had one malfunction about 4rds in and then it ran great for the next 45rds or so. I guess the gas block wasent lined up properly. Hopefully it stays working!!! Thanks again
Ryan |
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Quoted: Is the gas block up against the shoulder on the barrel? it should be spaced about 1/32" off the shoulder to align with the gas port ... it also could be the size if the gas port ... it might need to be opened up a bit. Bingo we have a winner! +1 for this advice |
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