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Thread: 7.62 bolt head to 5.56

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    Gunco Veteran muttman's Avatar
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    Default 7.62 bolt head to 5.56

    I have looked at the xm 9mm bolt head conversion and was thinking could this mod be used to make a 5.56 out of a rommy g bolt head. the case head size for a 7.62x39 is.445 and the case head on a 5.56 is .378 a diffrence of .067. I think with a ring made of 4130 tig welded in and recut of the case hole it could work. the only issue that could be a problem is the extractor. I dont know if a -74 extractor will fit a -47 bolt head. what do ya think??? muttman

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    Indian Admin Winn R's Avatar
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    I think I posted a pic the other day on this. But it's just a touch of tig both sides and turn the face down on the lathe.

    here it is:

    the extractor is also built up then milled but I don't think I have a picture.

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    Gunco Veteran muttman's Avatar
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    winn r,
    thanks for the post. could you post a link to " posted the other day" I could not find your post in this thred. I have a couple of Q's to ask and if I could read up first this might take care of a few, but for now what part of the bolt did you use to check to see if it was turning true? muttman

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    Indian Admin Winn R's Avatar
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    sorry -- this was an oh by the way here's another method to another thread.

    True on the shaft. The firing pin hole is centered.

    The extractor hole is cleaned up by hand. The '74 won't fit.
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    No Hope For Me 1biggun's Avatar
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    I personaly avoid any welding on the bolt or the trunion. even though the weld is small and all that I am a little worried about the posibility of cracks developing next to the weld and resulting in failure. A bulgy bolt is around $60 and it also has the spring loaded firing pin as well some thing else needed if you want to shoot 223. the weld on a 9mm conversion is a slightly different matter it is blow back so the lugs are not a concern and if it fails it is not likely going to cause a KB . This is all just my opinion. but for 60 dollars it is not worth the risk better to sell the 7.62 bolt and recoup some of the cost for the correct bolt. now if there were some way to attach a ring with low temp silver solder or a press fit maybe

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    Gunco Regular Gunter's Avatar
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    Ok, so let me ask an academic question. What would happen if you used the standard bolt with the .033 clearance around the rim? The only problem I can think of is if you got into really hot hand loads were you had brass flow. Just wondering.

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    Happy Camper hcpookie's Avatar
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    biggun I agree, however I wonder in this case if the AK lugs are heavy enough to compensate for any weld deficiency in the temper. It is "only" a .223 after all... I wouldn't do it for 30-06 or anything like that...

    Or here's a forehead-slapping thought - why not just re-temper the bolt? Or send it away to be re-tempered to someone with an oven?

    I like the idea of pressing in a ring - never thought of that one myself!!! If you do, you could drill/ream out the center of the 7.62 bolt and make it deeper so the "ring" would have more surface area to press against. Do it with about .005" press fit and you'd be all set!!!

    I have drilled out the bolt for a spring-loaded firing pin on my .308 build and it wasn't easy - that is some darned HARD steel! So keep that in mind if and when you drill it out for a ring or cup. If you make that ring from 4130 steel or something like that, I'm not even certain you'd have to heat treat the ring because it would be surrounded by the hard bolt. If you did heat treat it, I would harden it before I pressed it in.

    That ring is a really good idea.

    Another idea - are Galil bolts available? I haven't looked...

    I got a .223 bolt from Scott at DPH about a year ago. He may yet have some in stock. Just a thought. The bolt I got was an "AKM" style meaning it used all the "G" parts which fit perfectly. The extractor was easy and if you need to make a new one you can do so with a dremel and drill - just use a round steel shank or part of an old grade-8 bolt. Real easy to fabricate or modify one...


    Gunter it won't work with that much clearance. The extractor won't have enough "tooth" to pull out the rim and you'll just break off the rim, or it will just slide off without extracting. And it will happen randomly, making for a very frustrating build.
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    Indian Admin Winn R's Avatar
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    On the heat issue, the locking lugs operate from the rear. There's a substantial amount of material from the face to the rear of the locking lugs.

    The fill is two quick puddle welds on either side of the extractor hole. My welding is done by pros, they say it's not enough heat to change temper at the lugs.

    However, like so many other things with homebuilts, if you're not comfortable, don't do it.

    I would think the pressed in ring will be a bit difficult to keep in place considering the shock. We won't know until it's tryed.
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    If you cut the extractor hole in the press fit ring then wouldn't that make the ring a "C"? How would it stay in if not welded?

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    Gunco Veteran muttman's Avatar
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    winn r,
    you are correct on the tiging of the bolt head, thats the reason why tiging is used on high pressure hyd. fittings 4k psi and up.

    gunter,
    the idea was to tig in a ring made of 4130 and cut to make the slots for the ext/ ejector

    1biggun,
    if some form of heat sink is put in place and the bolt head is keept a 500+/- 50 deg. for 1 hr after welding the build up of hyd. gas in the weld will be removed giving a better weld. I dont think the side load on the wall of the "ring" or weldwould be to the point of case failure as long as the case wall is suported to failure of the ring/ weld. I am still way dehing the learning curve in guns thats the reason for the question.

    hcpookie,
    a press fit in that type of setting would not be that good. the chance of sliping is too great. a bolt head in 5.56 would be nice orf has some galil heads and kvar has the bulgy version at $100 to get one to my door is too steep for me at this point I could get one more kit for that price. the idea was to use a kit that I have and convert it over to 5.56.good call on the grade 8 bolt for the extractor.

    all thanks for the input I now have a better I dea of what and how this mod will be done. muttman

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