Hey guys,

I’ve searched the board for some info on this problem, but can’t seem to find anything.  Anyway, I’ve got 2 kits built (1 Romy G and 1 Polish U/F) but haven’t test fired them yet.

Without the FCG installed the BC slides nice and smooth on both AK’s.  However, with the FCG installed the BC begins to bind up and stick – both in the pull back and forward modes.  This occurs on both rifles.  The BC feels like it is sticking on the pull back in different spots.  When I release the BC it will bind up and stop completely and the handle has to be struck to make it go home into the lock up position.

I suspect that the hammer is putting upward pressure on the BC and causing this.  I was also thinking that the top rails might not be smooth enough and need to be polished a little.  One or the other, or a combination of both?

I’m sure someone has had this problem before me.  Suggestions/solutions?

Thanks!

Quoted: Hey guys, I’ve searched the board for some info on this problem, but can’t seem to find anything.  Anyway, I’ve got 2 kits built (1 Romy G and 1 Polish U/F) but haven’t test fired them yet. Without the FCG installed the BC slides nice and smooth on both AK’s.  However, with the FCG installed the BC begins to bind up and stick – both in the pull back and forward modes.  This occurs on both rifles.  The BC feels like it is sticking on the pull back in different spots.  When I release the BC it will bind up and stop completely and the handle has to be struck to make it go home into the lock up position. I suspect that the hammer is putting upward pressure on the BC and causing this.  I was also thinking that the top rails might not be smooth enough and need to be polished a little.  One or the other, or a combination of both? I’m sure someone has had this problem before me.  Suggestions/solutions? Thanks!

In my experience, that could be caused by the hammer spring tension.  If you pull the bolt and carrier out and cock the hammer back then push down on the hammer (towards the bottom of the receiver), you can feel how much tension there is to push the hammer down.  There is not as much tension on an AK that has been assembled for some time.  My theory is that the hammer spring is strong from not having had tension constantly pulling back on it for several years.  Once you assemble a new build, the spring, that has been relaxed for years, is now pulling the hammer forward with quite a bit of strength.  I believe that it will eventually work itself out, but I would keep the rifle stored with the hammer cocked to help expedite getting the spring back to normal tension so that the hammer moves down easier when the bolt carrier slides across it.  If you have a weaker hammer spring with less tension, you might be able to substitute it and have the bolt slide easier.  Really, it could be caused by several things, but that's the most likely, in my opinion.  

I'll try that or take the spring from my WASR (which doesn't have this problem) to see if it works better.

My Polish UF is a bit stiff as well.  I'm pretty sure it's the hammer pushing upwards on the BC.  It's definitely gotten better though I think, just run a couple hundred rounds through it and see how it works afterwards

I believe from your description you've narrowed down the problem to a couple possibilities; specifically saying that the bolt carrier works fine with the trigger group removed (which almost eliminates the bolt carrier or piston being goofed up).  

If you pull the bolt back all the way to the rear and let it slam forward does it hang up?  If not, that's perfect.  Don't ease the bolt forward as it can hang up on the trigger group as the hammer pushes up a bit on the bolt carrier.  Just pull it back and let it slam forward - if it doesn't hang up that way - you are in good shape.

Also, make sure you didn't put the hammer in backwards.  

what kind of receiver are you useing?

did you have the bolt in the carrier when you tested it without the FCG in?

And after?

where exactly is it hanging up on closing? (can you give an exact distance from closed?)

Quoted: If you pull the bolt back all the way to the rear and let it slam forward does it hang up? Yes, it hangs up when I do this.  It seems to bind mostly at the point it rides over the hammer and other time a little further forward (~ 1in. from lock-up). Also, make sure you didn't put the hammer in backwards. Thought of that and checked it – I didn’t.

Quoted: what kind of receiver are you useing? AK-Builder bent flat. did you have the bolt in the carrier when you tested it without the FCG in? Yes, I checked it with and without. And after? I haven’t tried it without the bolt in, but will do so. where exactly is it hanging up on closing? (can you give an exact distance from closed?) See my response to Black-Wolf above.

Who's bending jig did you use?

I bought a bending jig here on the EE a year or two ago and bent a bunch of flats, and built one... only to find out that it was made about 1/16" to 1/8" too short, which made the top rails way too close to the fire control group.  I had to take it to a machine shop to get extra material welded on and then milled down to the correct dimensions.  

Check your receiver height at several places against a blueprint.

Quoted: Who's bending jig did you use?

DPH bending jig.  I haven't heard of any problems associated with their jig.

Quoted: Quoted: If you pull the bolt back all the way to the rear and let it slam forward does it hang up? Yes, it hangs up when I do this.  It seems to bind mostly at the point it rides over the hammer and other time a little further forward (~ 1in. from lock-up). Also, make sure you didn't put the hammer in backwards. Thought of that and checked it – I didn’t. Quoted: what kind of receiver are you useing? AK-Builder bent flat. did you have the bolt in the carrier when you tested it without the FCG in? Yes, I checked it with and without. And after? I haven’t tried it without the bolt in, but will do so. where exactly is it hanging up on closing? (can you give an exact distance from closed?) See my response to Black-Wolf above.

I've got a dollar says your ejector is to long. The 5.45 ejector is about 1/16" longer than the 7.62 ejector.

Most flats come with rails that are "multi purpose" and if you are building a 7.62, you have to cut a little bit off them. \

One inch from lockup means that the bolt is already in the trunion, so it is not a rail/trunion alignment problem. It also means that the bolt carrier is almost to the ejector.  

here is what happens, as the bolt slides along the "to long ejector", the ejector pushes the bolt to the right, and causes it to hit the trunion. This does not always cause the bolt to stop, (usualy, in fact)  the bolt will simply ride past the trunion/rail interface, because, the bolt has enough slop (the shaft fits loose inside the BC)to move over to the right a little, thus compensating for the ejector sticking out to far.  . The problem comes when the bolt carrier gets closer to the ejector. that "slop" has less play (because the bolt has more play at the front) The bolt carrier pushes against the right side of the rails, and thus forces the bolt agaist the ejector.

The fact that the gun still closes with a tap shows that the AK design is loose... but not THAT loose.

You can verify this by

1: turning the gun upside down (and/or take off the top cover) , and watch the ejector closely as you slowly close the action by hand (no spring installed), as the ejector passes into the bolt groove, it will force the bolt to move to the side. As the ejector gets to the BC slot, that slop goes away, and the binding starts.

2: put the bolt face even with the ejector, there should be a "very small" gap there

You are also feeling the hammer riding against the bolt, but this part is normal. the hang up is caused by a to long ejector. trust me...

Still stumped guys.

I didn't have much time to mess with it last night (daughter's PTA meeting took most of the evening).  Anyway, I rechecked my Romy G as it binds up the most (especially just over the hammer).  

I checked to see if the bolt was impinging on the extractor - with the cover off, the spring both in and out, and the rifle both right side up and upside down.  It didn't appear the the extractor was causing the the bolt to move to the right.  There isn't much space between the area where the bolt meets the extractor, but it didn't appear to be the cause.  So, I thought it might still be the top rail.

I took my digital calipers and measured the interior rail width front to back and found a very slight narrowing towards the rear.  When checked against the bolt width where the rail fits inside it was about .004 too narrow at the rear.  I filed the top rail down to be even along the full length.  It still binds as before, if not a little worse, however the top rails are now rough and not as smooth as before.  I didn't have time to smooth them down.

The hammer pressure is still very stiff against the bottom of the BC, which is the point it binds up almost every time.

Hopefully, I will get some time this weekend to work through all of your suggestions.

I appreciate your input.

Quoted: Still stumped guys. I didn't have much time to mess with it last night (daughter's PTA meeting took most of the evening).  Anyway, I rechecked my Romy G as it binds up the most (especially just over the hammer).   I checked to see if the bolt was impinging on the extractor - with the cover off, the spring both in and out, and the rifle both right side up and upside down.  It didn't appear the the extractor was causing the the bolt to move to the right.  There isn't much space between the area where the bolt meets the extractor, but it didn't appear to be the cause.  So, I thought it might still be the top rail. I took my digital calipers and measured the interior rail width front to back and found a very slight narrowing towards the rear.  When checked against the bolt width where the rail fits inside it was about .004 too narrow at the rear.  I filed the top rail down to be even along the full length.  It still binds as before, if not a little worse, however the top rails are now rough and not as smooth as before.  I didn't have time to smooth them down. The hammer pressure is still very stiff against the bottom of the BC, which is the point it binds up almost every time. Hopefully, I will get some time this weekend to work through all of your suggestions. I appreciate your input.

santanatwo makes a good point that it could be that the extractor is too long.  In my experience with my most recent completed build, I had the exact same problem as you describe, but I left the hammer in the cocked position for a couple days, and now the action is much smoother.  It no longer binds up, but if I ride the bolt carrier home, it will stop at the same point.  Many normal AKs will stop if you ride the bolt carrier forward, so I'm not particularly worried.  I'm taking it to test fire soon.

Your point about the rails not being perpendicular is something to consider also.  On a build I completed, one rail was slightly elevated in the back, and I ground the top of it down with a Dremel.  While this effectively made the rail thinner, it's the only thing that could be done to get the bolt to slide.  To be sure, you should force the bolt open and closed a couple times, and then check to see where there is shiny, raw metal.  If it's on a rail, then that may indeed be your problem.

have you tried deburing and polishing the rails?

Burrs form when you trim the rails... take some progressively finer grit and wet sand/debur/polish the rails.

The smallest burr on the rails can make a big difference.

Are you using a G2 FCG?  If so, that's probably the reason.  G2's are notorious for having boltcarriers get caught on them.  You can either see if firing a few hundred rounds breaks it in enough to stop the hangups or take a dremel and grind down and then polish the profile of the hammer.... you don't need to take off very much and don't grind off any part of the hammer that actually comes into contact with the rear of the bolt when hammer is released.

Quoted: Still stumped guys. I checked to see if the bolt was impinging on the extractor - with the cover off, the spring both in and out, and the rifle both right side up and upside down.  It didn't appear the the extractor was causing the the bolt to move to the right.  There isn't much space between the area where the bolt meets the extractor, but it didn't appear to be the cause.  So, I thought it might still be the top rail.

That's not what santanatwo said.  re-read his post.  It's the bolt carrier binding on the extractor, not the bolt. good luck.

If you are using a TAPCO G2 hammer, that is very likely your problem.

See:
ak47.net/forums/topic.html?b=4&f=51&t=95026

If you don't want to work on reshaping the hammer profile, consider a Wolff extra power recoil spring.  I sold about 20 of them to folks with your problem.  Most were Romy builds but be advised one Romy build suffered from stove piping because the spring was actually too strong for his build.  I also don't recommend a recoil buffer with an extra power spring.

To positively narrow it down to your G2 hammer (if that's what you have), swap it out for the original hammer and verify that with the original installed, your problem is fixed.

HTH

Quoted: Quoted: Still stumped guys. I checked to see if the bolt was impinging on the extractor - with the cover off, the spring both in and out, and the rifle both right side up and upside down.  It didn't appear the the extractor was causing the the bolt to move to the right.  There isn't much space between the area where the bolt meets the extractor, but it didn't appear to be the cause.  So, I thought it might still be the top rail. That's not what santanatwo said.  re-read his post.  It's the bolt carrier binding on the extractor, not the bolt. good luck.

No, I was saying it could be the bolt carrier binding on the bolt as the bolt binds on the ejector.... (it's a three part problem, caused by the ejector being to long)

Okay guys, I finally got some spare time to work on my builds after letting them sit for a few days with the hammers in the cocked position.  This alone seems to have improved them somewhat, as they weren't sticking as much as before.  I also smoothed and polished the top rails, which (at this point) seems to have eliminated the problem.  

I still have not had time to test fire the rifles, so I won't know for sure if the problem has been fixed until then.  I have not dismissed the possiblity that the hammers may still need to be modified and will look at that if the problem persists after firing.

Thanks again for all of your inputs.  I LOVE this site!