AK bolt hanging up

[krazz]

I'm on my 3rd build, and this time I'm using an ITM MK99 receiver (which in comparison to NDS....sucks). I've got her all put together, headspaced and ready to test-fire before I spray her with Duracoat Tac Black.

When manually cycling the bolt carrier with bolt (firing pin removed), the bolt hangs up at the trunnion. I've ground down all the rails slightly, and given everything a nice polish, but she still hangs up. It looks like the bolt isn't sliding into the trunnion true. When it locks up, the bolt is canted at a slight angle right at the left side locking lug.

It's hard to explain this without pictures, so I'll try to post some tonight if there is any interest.

I was also thinking it might be something with the carrier allowing the bolt to rotate back just a bit when sliding forward. I say this because when I point the gun muzzle down, and let gravity take the carrier home, there are NEVER any issues. When I place the gun muzzle up, it ALWAYS binds, and when she's level, it's hit and miss.

Any help from you AK gurus would be appreciated.

[Ford8N]

It could be several things. If it is hanging up just before it goes home check to make sure the piston isn't hanging up at the gas block. It could be canted just enough to muck things up. Also the hammer might be to high. On cheap receivers the trigger/hammer pin holes will be out of spec. Also try putting a mag in and see if it will cycle some dummies. It might not work empty but will work with dummies. That way you can also check to make sure the mags are at the correct height. What year kit? Certain vintage kits were out of spec because of internal political times at the plant. This is all I can think of at the moment with the info you provided. Good luck!

[krazz]

I'll check that out tonight, I'll take a look at the piston....I think it's a '72, but I could be way off. Thanks.

[motorhead]

are the lwr. rails level with the trunnion? they can be bent up SLIGHTLY. massive misalignment requires removal/rewelding.

[JamesY]

Does it also hang up when you have it fully assembled and let it slam forward on its own?

[krazz]

Well, to answer questions, it hangs up either fully assembled or stripped, with the mag and without, with ammo and without. The only time it doesn't lock up is when I cycle it muzzle down.

That being said, he problem lies with the bolt. What EXACTLY the problem is, I don't know, but I changed the bolt out for 4 different others from different kits, and there wasn't a problem. The bolt seems like it's a little sloppy, but they ALL seem all little sloppy.

I really want to find out what's wrong, so if I find anything out, I post it.

Thanks for the help.

[Brendan Sullivan]

Initial thought was rails interfering with bolt as it rides into trunnion. Maybe the ejector on this receiver has different dimensions and is pushing the bolt to one side as it tries to lock? Have you taken the offending bolt and tried the same tilt test in other AK's?

[bigbob76]

1. Is the piston bent on the bolt carrier that hangs up?

2. I've built a lot of rifles and I've been able to laugh at myself for some of the things I couldn't figure out right away. I have had dented gas tubes, gas tubes that weren't completely seated in the rear sight bases etc.

3. Have you removed the recoil spring assembly and watched very closely what's happening as you slide the bolt carrier back and forth?

[SVT-40]

Check the ejector slot on the left side of the bolt. I had a bolt in a Bulgarian kit where the slot for the ejector was not properly milled. Compare the slot in the problem bolt to the slot in a bolt that functions properly. If the slot is the problem use a small file to shape the proper profile, matching the slot in the bolt that works.

That is my bet on the problem.

Look at the bolt face. The slot should be nice and square. The slot should be smooth and run the entire length of the bolt, except the last Approx 1/2"

If the slot is not deep enough the ejector will be riding against the ejector slot in the bolt and push the bolt to the right. This can cause the problem you have as well as mis feeds from the left side of the magazine on some rifles. Especially rifles where the mag is wobble or installed "low"

Install the bolt in the carrier and slowly try to shut the bolt. Look at the bolt from the bottom of the receiver viewing the ejector area through the mag well. Watch the problem bolt as it passes the ejector and then try it with a bolt that works. You may be able to see the issue.

[krazz]

Well, the problem lies in the extractor retaining pin. It juts out a very small amount even with the firing pin retaining pin installed. I push it in, and everything cycles fine, but after 10 or so cycles, it pushes back out and jams. Here's a picture of the offending bolt(left) next to a almost new Romy bolt(right).

http://www.calguns.net/calgunforum/attachment.php?attachmentid=49390&stc=1&d=1268793774

Thanks for all the help. I'm going to completely disassemble both bolts and see if I can further pinpoint the problem.

[motorhead]

new pin. kvar.