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Discussion Starter · #1 ·
Nhm 90 took to range and after firing about 250 rounds the bolt starring getting stuck closed. Had to use my metal ammo box top open it. Field stripped didn't see anything obvious. Fired more but kept getting stuck had to call it a day. Took apart at home and found that the gas piston is getting stuck in the gas block. I cleaned and lubed then cleaned add lube and got it to where is wasn't sticking anymore. Also, when it was sticking the blot would almost clone but I still had to force it closed maybe 3/16" and then it would be stuck in. It's ok now but I'm sure it will happen again next trip. What the heck is going on? Why is the piston getting stuck in the gas block? Anyone ever have this problem? How do I fix this?
Don't want to buyou another ak bit now I can't rely onyou most reliable rifle anymore. Bummer
 

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I would take it apart 1 more time all the way down to the extractor, clean, lube and reassemble.
Check for fit by moving all the parts in position by hand and feel for binding.
I don't think 250 rounds are that many and would not think that would be an issue.
 

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Check to be sure the rails are straight and don't have an elevated area.
 

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so when its stuck could you wiggle the back of the carrier? i would think the gas piston would have some major marks on it if that is what is actually sticking.
take any measurements or the gas block id/piston od?
 

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First of all, look down the back of the rifle. Does the rear sight, gas block, front sight look straight? Is the gas block crooked?

Then pull the gas tube off(recoil spring in) and press down on the carrier so it runs flat on the top of the receiver and see if its *generally* running straight in or if its way off and hitting the rear sight base or gas block. Let us know.

Look at this video

The gas tube helps guide the piston into the gas block, however if the difference between your rear sight base and your gas block is too slanted in either direction, it could hang up.

Also, with the top cover off while manually cycling it(maybe dry?) try to feel where it is hanging up.
 

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Pictures if you need more help in the trouble shooting department.
 

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Discussion Starter · #8 ·
When it was hung up the bcg had play and would wiggle a bit. The only thing that didn't have any play was the piston in the gas block assembly. Took the handguards and piston covet off to inspect. Since I cleaned the end of the piston and the inside of the gas block which didn't look bad at all I can now rack it and it won't get stuck. Looked like the gas block tube had no clearance for the piston. There are some marks on the bolt carrier that enter the sight and barrel block. But all the sticktion was in the gas block and the piston getting stuck. I may slightly sand the piston with some 1000 grit just a little to make the diameter smaller but everything else looks strait ad an arrow to me guys. Idk I'll keep you posted next range day. Thanks for all of your replys I'll let you know what I come up with.
 

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Discussion Starter · #9 ·
Another thing. While firing the gas tube cover locking arm kept coming loose. I'm suspecting the gas tube was moving and guiding the pistion in crooked and caused some problems. I modified my gas tube to but on a handguards with a pI cations rail. I removed the lips that held in the wooden handguard in place but was in the way of putting on the aluminum handguard. May need to but a new gas tube mine has the holes in the tube originally so I'll need to find one and see if that helps and get a better grade handguard for my accessories.
 
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