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Discussion Starter #1
Hey there, long time lurker first time poster. So, I just finished building my first kit, a fully matching fixed stock Polish AKM. Did the deal proper, used a rivet jig and hydrolic press and the whole shebang. She's a beaut :)I headspaced the virgin barrel using CIP go and no-go gauges, populated the barrel, and everything seemed fine. Took her out to shoot her tonight, first 5 rounds ran clean, no FTFS, cycled perfectly. After the first 5 rounds, I checked the headspace again, just by inserting a no-go gauge in through the ejection port, and lo and behold, the bolt carrier closed on the gauge. I immediately popped the hood off, removed the bolt carrier group, and inserted the no go gauge, this time trying with just the bolt. Nowhere NEAR closing on the gauge, try as hard as i could. Inserted the carrier group. Still would close on the gauge, but I had to put a little stress.

Needless to say, I took it home without shooting it any more for further inspection. I don't want to see a KB, and I can always re-headspace the barrel if need be. In the brighter light of the garage, I examined it more closely. It seems that although the bolt is not locking on the no-go gauge, the carrier (if forced, or hot from a few rounds being fired) will somehow slide OVER the bolt, and come flush with the trunnion without the bolt completing the end of its rotation. Here's my question: is this dangerous? What is going on here? It seems like the bolt and carrier move as one unit, so how is the carrier sliding forward without the bolt rotating?

If someone could tell me what's going on here, I would really appreciate it. I mean, this thing is going to be near me and my girlfriend's face. There's no way I'm shooting this puppy if there's a chance it's not safe.
 

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Do you have a field gauge? It sounds like you are within the proper tolerances. I test mine by hand with the bolt only and remove the extractor. When I put the carrier in, I always faced the same issue as you do. It would appear to close on the no-go, but the bolt wouldn't quite finish it's rotation.
 

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Discussion Starter #4
I don't have a field gauge, unfortunately - and I'll take some pictures and a video when I get home, I'm at work now. I should clarify that the extractor and fp were removed when rechecking headspace when I got home. Thanks for the responses :) I'd love to hear a couple more people chime in. My understanding is that while I run the risk of sounding paranoid, there is no such thing as "too safe" when it comes to headspace.

Here's my one concern, and it may be unfounded: If the carrier closes home on a round, but the bolt doesn't lock fully, the little tail on the rear of the carrier is now out of the way of the hammer hitting the fp and causing an out of battery discharge. Unless there is another way the ak prevents an OOBD? Seems like not, since there's no hammer retarder in the semi-auto models.
 

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No-go headspace gauges should give the appearance of almost closing, but should not allow the bolt to fully close. It sounds normal to me, but as others have said it would help to see pics.
 

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Discussion Starter #7
Again, the bolt does not fully rotate into the locked position, still a good 1/4" of clearance between the top lug (? don't know the technical term) and the side of the trunnion - the bolt itself is not closing, but the carrier is proceeding all the way forward (if given a little pressure). I'll take a video when I get home.

One thing I noticed, is even when the carrier is not locked all the way forward (NOT pushed up against the trunnion), the tail on the back of the carrier is still not long enough to prevent the hammer from hitting the bolt/fp. So it seems like it only prevents a OOBD if it is going to occur way before the bolt and carrier get into the locked position. Interesting. Guess it's just that much more important to get the headroom right :p
 

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Here's a good example, see the bottom where they check the headspace - that's about what it should look like.

M1 Garand Part Inspection
 

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Discussion Starter #9
Here's a good example, see the bottom where they check the headspace - that's about what it should look like.

M1 Garand Part Inspection

Now here's the thing - on the ak, the bolt is not exposed as it is covered by the carrier when locked into battery... although I'm sure the bolt is not locking up. From everything I'm reading, it seems to not be a problem that the carrier comes all the way forward as long as the bolt does not positively lock up
 

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Yes, the carrier isn't really built to be that tight, so the minute amount that the bolt is out of battery won't really stop the carrier from being fully forward.
 

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Also remember that when using headspace gauges you don't force the bolt. LIGHT pressure only until it stops. It sounds as though your headspace is fine. You may be causing the issue yourself by using too much force on the bolt carrier.
 

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Discussion Starter #12
Also remember that when using headspace gauges you don't force the bolt. LIGHT pressure only until it stops. It sounds as though your headspace is fine. You may be causing the issue yourself by using too much force on the bolt carrier.
I did not know this. If that's the case, I should be fine. I do have to put pressure to get the bolt carrier to close. I learn new things every day :)))
 

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Well if you are closing on the no-go that would indicate excessive headspace and the risk would be blown primers or case head separation/blowout. The out of battery incident you address would be more likely caused by to little or to tight headspace. IE: round chambered but bolt not fully locked and then fired.


Sounds to me yours is a bit loose but still in spec.

What do your fired cases look like? Are there any bulging primers or case deformation?

Excessive headspace will show up in your cases with bulging or blown out primers and/or swollen cases, hard extraction/ripped off case bases etc.
 

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Discussion Starter #14
Again, the headspace is well within spec when checked with just the bolt. It is the carrier only that is sliding home. The bolt itself stays open on the no-go gauge, but the carrier itself will close. I haven't checked my fired brass, I'll do that tonight. Unless I see bulged primers or split cases I'm going to figure all is well here :) Thanks to everyone for your help
 

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The bolt carrier should close on a go gauge with no more than 33 pounds of gentle pressure. The carrier should not closes on a no-go with up to 66 pounds of gentle pressure. The carrier has closed if it has contacted the trunnion on the left side. So if you are putting less pressure then that on the carrier and it is closing on the no-go then that does not sound good. I think you are correct to be concerned.

Have you made sure that the bore is completely spotless when checking headspace? Same question for the bolt face, and the lugs on the bolt and trunnion. The difference between a go and a no-go gauge is about .0045" so debris the size of a human hair could cause issues.

You said there is still 1/4" of clearance from the triangle lug on the bolt to the trunnion with a no-go gauge, that sounds correct when just using the bolt. How close does the triangle lug come to the trunnion using a go-gauge? In my experience there is usually a small 1-2mm gap on factory rifles but that still provides a full lock with the bolt carrier.

What country made your trunnion, bolt, and bolt carrier? Are all three numbers matching from the same original rifle?
 

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Sounds like after the first rounds were fired the barrel pushed forward up against the pin, I dont know why this happens but remember reading about the possibility of it happening on home builds.
 

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The locking lugs in the trunion and bolt should ALWAYS be lapped to each other before head spacing! Otherwise any bur or paint could throw the gauge off, and it is important to insure that BOTH lugs share the load equally.
 

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I have nothing to add as I agree with the advice here.

Mostly I want to thank Walleye for that Garand link, I am going to use it during my yearly Garand teardown. Thanks.
 
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