AK-74 headspace adjustment.
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Thread: AK-74 headspace adjustment.

  1. #1
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    AK-74 headspace adjustment.

    A while back I built a Bulgarian AK-74 from a parts kit. At the time I didn't have a "Go Gauge" but I did have a NoGo so I used a live round as the "GO". Pretty stupid mistake. I took it to the range and the cases showed High pressure signs.. The ammo I was using had bullets .003 over the size of the bore. So I thought that was my issue. I went out to the range and used the proper bullet size ammo and didn't show as bad pressure signs but it was still cratering the primers. I borrowed a 5.45 Go from a friend and the bolt won't close all the way on a Go probably about .002 left of travel on the bolt. Is there any way I can adjust this distance without pushing the pin and barrel and drilling an oversized pin? Can I use fine lapping compound to take material of the back of the lugs, or will this compromise the hardness of the bolt? Thanks for your input and time.

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    are you using hand-loads?
    Need some gun-smithing, refinishing work done? Shoot me a PM.
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    Just put the bolt face down in a vice and file the back of the lugs.
    Carefully...
    You want to obviously file in the same plain as the lug and you can tell you're doing this by the surface after each stroke.
    It might only be a couple strokes on both sides evenly.
    You could also use a wet stone after a couple strokes to smooth it up.
    And a little lapping compound and built cycling when you're done.
    This will tell you too how much contact you're getting between the surfaces.
    I want add, go slow. If you start with ten steps I bet you'll have gone to far. Do a couple on each lug and check headspace to get a feel for how much closer you are.
    Leave it right so you can stone/lap it in the rest of the way.
    Last edited by BR7.62; 11-21-2018 at 10:30 AM.
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    Quote Originally Posted by dnepr0mike View Post
    are you using hand-loads?
    No, using Hornady 5.45x39

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    Quote Originally Posted by BR7.62 View Post
    Just put the bolt face down in a vice and file the back of the lugs.
    Carefully...
    You want to obviously file in the same plain as the lug and you can tell you're doing this by the surface after each stroke.
    It might only be a couple strokes on both sides evenly.
    You could also use a wet stone after a couple strokes to smooth it up.
    And a little lapping compound and built cycling when you're done.
    This will tell you too how much contact you're getting between the surfaces.
    I want add, go slow. If you start with ten steps I bet you'll have gone to far. Do a couple on each lug and check headspace to get a feel for how much closer you are.
    Leave it right so you can stone/lap it in the rest of the way.
    Ok sounds like a plan. I'll followup on the results. Thank you so much for the help.

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    Pics of cratered primers?

    Honestly, given that you are new to building, and maybe to avoid creating new problems, I suggest starting over head spacing with an oversized bbl. pin and reamer https://ak-builder.com/index.php?dis...oduct_id=30059 . Use both your No-Go and your friends Go gauges this time.

    This may be a good lesson to home builders. Fabricate or improvise all the tools you want but at least get a set of headspace gauges in whatever caliber you are using. The are relatively cheap compared to ruining a firearm or imbedding chunks of metal in your face.

    Don't take the above as picking on you OP. Nobody is perfect, (well maybe except Mr. Nobody and that sweet Type-1). I'll gladly admit to messing up a few bbl. pins and more.

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    Here are some pictures of the cases. Total of 10 samples(these are the worst ones out of 20 shot) . No split case mouths.

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    One other quick think you can try.
    Are you using a press to build?
    If you put the rifle in the press, you need barrel push out to like Forbus sells.
    Leave the pin in and try to push the barrel out.
    Not with more pressure than you would actually use. Then small the press plates with a hammer when the pressure is applied.
    You might shock it the couple thou that you need.
    Remember if you end up pulling the barrel you might want to nudge it in slightly before trying to push the pin out.
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    Do what Br posted before you try lapping lugs or resetting the headspace.

    So to clarify the bolt is just slightly off from closing on a go gauge but will close and fire with the several live types of ammo you tested?

    On your primers, does your bolt face have chamfered firing pin hole? I would suspect that as the cause of the fired primer shape. Unless it is extreme I don't think it is an issue.

 

 

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