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Discussion Starter · #1 ·
Posted this about a week ago over at AK-47.net.
http://www.gunsnet.net/forums/showthread.php?s=&threadid=163387
My AMD is not fully cycling and after further inspection, it appears that my carrier is rubbing hard against the gas piston hole. This is the only thing I can come up with, my lower rails are fine, I changed redstar arms adjustable trigger to a tapco G2 where the hammer doesn't have any sharp points. and the carrier and rail travel smooth with hand operation. But when I pull up a little when I cycle the gun it hangs up. When firing this weekend and it jammed I took it apart and noticed the carrier was very tight against the top of the gas tube opening. What is the best way to correct this? Will tapping the rails down slightly give me anymore clearance or do you think I should dremel a little on the opening? This is a home-bent receiver so my rails might not be exactly horizontal and square. I think I probably should start modifing to them first.
:confused:
-Tim
 

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take a carefull look at the rails. The end of the rail should be flush with the trunion lugs. this way the bolt carrier will transfer smoothly off the rail and onto the lug. If the rail is a bit too high this may cause what you are describing. dose it look like the top of the rail is rubbing their. KEEP in mind if the rail is too low the carrier will not come back smoothly or at all. I have found vulcans are often too low and need to be adjusted up a couple MM to transfer smoothly.
Also check that the rails are equil distance from the top all the way and not ramping up or down to the trunion
this may not be the answer but they will give you a place to start.
you say it is an AMD ,, is it a 65 or a 63??? is it a seem to be matching number kit?
I would not put the dremil to it untill I had eliminated all other posibilitys. not saynig dremmil is bad but I hate to find something simple after grinding :)
I think others guys will have other places for you to look too
 

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Happy Camper
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Romack991,

I think I understand your problem - let me get this straight - you are experiencing the binding between the carrier and the gas piston hole - does that mean that the END of the carrier piston is rubbing against the gas block when the carrier group is put into battery (all the way forward)? Or am I misunderstanding?

If I am understanding this correctly, then it could be that your gas block's hole is smaller in diameter than the piston. I had this exact problem on my AK-103 build when I bought my AK-74 style vertical gas block from k-var. This was a brand-new never-used gas block, so I even had to drill the holes for the retaining pins.

In my situation, I found out that the hole the end of the piston seats into was smaller than my piston! This prevented a "smooth" insertion of the carrier group into battery. I took the dremel to it w/ a medium, then fine, stone, and when it finally seated correctly, all worked as advertised. There is some slop here, so you should see the rear-most end of that block is larger and "ramps" into the smaller diameter. Be careful with this, because if you screw it up by making it too large, you'll need a new gas block... not a fun process. Go slow, use a fine stone, and test often.

Or am I mis-understanding the description of the problem? If you are talking about the carrier body rubbing against the top of the tube where the handguard is set, then the rails themselves may be too high.

hth,
- Jerry
 

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Happy Camper
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Romack,

Thanks for that clarification! That definitely negates my first idea about the gas chamber... so it is the space under the rear sight block that is rubbing... hrmmmmm..... If I read your description it is on the top, correct? Can you take a sharpie or dyekem or something to see the rub pattern, and if there are any other locations that are jamming the carrier into this section?

A few thoughts....

- Front trunion screws are causing the barrel to be "canted" upwards, so that the muzzle is higher than the breech.

- Front trunion screws are causing the barrel to be pointing off-center to the left or to the right, causing interference.

- Rails are slightly canted... can you verify measurements on the front compared to the back of the rail clearance? As I recall, it is a drill bit size #C that you need for clearance.

- Rear sight block is canted to the left/right, causing just enough clearance issues...

I get the feeling that if any of these apply, then somewhere, there is a hole that will need to be welded in, then re-drilled... if it is the rails then you may have enough material to drill new holes and just fill in the old holes with JB weld or simply weld them up w/ a TIG/MIG etc.
 

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Happy Camper
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I don't think I would tap down the rails, because you would probably just move the problem somewhere else...

If it happens to be that there are some mis-aligned holes, and redrilling holes isn't an option, then if it were mine I would consider dremelling the top of the openeing in the rear sight block. You can get a new rear sight block if needed but it is a booger to put back on so this may be even more work! I would consider using the dremel only after you're sure that there are no other options.
 

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In looking at your picture and the fact that it is a home-bent receiver, I say that your problem lies with the top rails. The bend at the rails doesn't look real sharp in the photo. The bend at the top rails should be a sharp 90 degree bend. At any rate you definately want to make sure that the top rails are flat and that they mesh perfectly with the trunnion or severe binding will occur. Tapping the top rails down will only work if you can keep them flat and maintain the proper gap between the upper and lower rails.
 

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Best Guess:
When hand cycling it works fine right? But when you pull up or apply pressure underneath the carrier when it is going forward (like in actual operation due to carrier pushing down hammer) it binds.

One would think that the pressure on the carrier from the hammer would possibly bind it, but maybe it actually helps cant the carrier front down. But when a loaded mag is inserted you have another pressure point, so that might be why it is then binding up.

Factory AK's and good bents have the top rails actually bent down on the inside slightly. You may just have too much slop on the top rails, so tapping them down could possibly correct the problem.
 

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If everything else appears to be correct, some light massaging of the top of the bolt carrier, may be the answer.

Did you change the piston, or is it original?
 

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Discussion Starter · #11 ·
I hammered the top rails a little and now it usually will eject the round and isn't binding up on the rear sight block. But it doesn't seem like the carrier is still going all the way back. I keep getting misfeeds from the bullet not catching appropiately. I think the carrier is hitting on the relief slot for the bolt. I think I may have made this slot slightly to large. The plan right now is to start on a new receiver and if this one bends sharper, which it should since I've changed my jig some, just replace this one and chalk it up to experience. Its only 2 bucks worth of sheet metal.
 

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I've heard other people have used a buffer to cure that problem.
It keeps the carrier from going back far enough to get hung up on the slot.
 

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I had this problem with a Norinco AK years ago. All I did was to file the rail slot in the bolt carrier. I made a cut on the front of both rail slots that was wide open and tapered back into the regular rail slot sot that it looked like this ---<. This allowed the bolt carrier to ride up a little in the cutout but be able to move forward and align itself on the rails when going back to battery. If I recall, I only opened up that last 1/16-1/8 inch of the rail slot. Not much was needed.

I would do this only of a buffer won't work to fix the problem.
 

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Tim-

To answer the question of how far back is the bolt going, place a piece of masking tape or tape a piece of paper between the cover and the receiver to the rear of the charging lever. Fire the rifle and see how far back the paper or the tape is torn.

I don't quite follow what's happening with the " bullet not catching appropriately". I think you mean a failure to feed where the cartridge is not being stripped out of the magazine. There's another thread here on that same subject which agrees with my experience that the rear of the magazine needs to be lifted a little. That can be checked by loading a full magazine, firing the rifle resting on the bottom of the magazine ( forcing the magazine upwards) versus firing the full magazine unsupported.

 
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