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7.62 bolt head to 5.56

2K views 20 replies 7 participants last post by  muttman 
#1 ·
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
 
#2 ·
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.

 
#3 ·
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
 
#4 ·
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.
 
#5 ·
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
 
#6 ·
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.
 
#7 ·
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.
 
#8 ·
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.
 
#9 ·
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?
 
#10 ·
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
 
#11 ·
So when are we going to get serious about US-build bolts? We have them for AR builds... just thinking aloud. That rotating lug is the only thing on a bolt that has me puzzled. The rest is just lathe and mill work. And of course heat treating.
 
#13 ·
Rotating Lug ??? now I'm confused I thought the whole bolt on an AK rotated.

The AR has rotating lugs but they're just cammed by the carrier like an AK.

Home made bolts, I like it, and the front trunions would not be to difficult to make either, bullet guide looks to be more work.
 
#15 ·
as far as it just being a 223. the 223 has over 50,000 psi or about 54,000-56,000 CUP. and even though the rim is smaller and it will reduce the bolt thrust some it does not reduce it a lot (some were here there is a formula for figuring it out.) If I remember right the bolt thrust was higher than the 7.62 x 39.
I tig weld and all other types as well and passed a certifed welding test 20+ years ago before I actually welded very well at all it is not that hard (No I do consider myself certifed or am I currently certifed). I also have some back ground in metalogly and failure analsis. for any thing to be welded the parent metal has to become molten and that is going to change the structure of the metal that area can act as a stress riser and a crack can devlope. even if a heat sink is used you still have to get the area hot enough to melt were the welding is being done. that spot is going to be different than the rest of the bolt. if it will fail I have no for sure way to say yes or no ( it likely will not) but I do feel it is more prone to fail after a part of it has heated up and had the temper changed . yea the Kvar bolts are a little pricey but I orderd 3 at a time and the bulgy5.56 mags and the 5.56 bullet gude and all the extra pins and crap that I think I will need so the shipping is not a big deal. and again you also need to have a spring loaded firing pin if you plan on shooting comercial ammo so figre all that in as well. as stated above dont do it if your not comfortable so again this is why I dont do it. sorry for the typeos It is late and I just got done loading 500+ round of 223 on a single stage press and Im tired.
 
#18 ·
1biggun said:
as far as it just being a 223. the 223 has over 50,000 psi or about 54,000-56,000 CUP. and even though the rim is smaller and it will reduce the bolt thrust some it does not reduce it a lot (some were here there is a formula for figuring it out.) If I remember right the bolt thrust was higher than the 7.62 x 39.
I tig weld and all other types as well and passed a certifed welding test 20+ years ago before I actually welded very well at all it is not that hard (No I do consider myself certifed or am I currently certifed). I also have some back ground in metalogly and failure analsis. for any thing to be welded the parent metal has to become molten and that is going to change the structure of the metal that area can act as a stress riser and a crack can devlope. even if a heat sink is used you still have to get the area hot enough to melt were the welding is being done. that spot is going to be different than the rest of the bolt. if it will fail I have no for sure way to say yes or no ( it likely will not) but I do feel it is more prone to fail after a part of it has heated up and had the temper changed . yea the Kvar bolts are a little pricey but I orderd 3 at a time and the bulgy5.56 mags and the 5.56 bullet gude and all the extra pins and crap that I think I will need so the shipping is not a big deal. and again you also need to have a spring loaded firing pin if you plan on shooting comercial ammo so figre all that in as well. as stated above dont do it if your not comfortable so again this is why I dont do it. sorry for the typeos It is late and I just got done loading 500+ round of 223 on a single stage press and Im tired.
1biggun,
I agree with your statment "if you dont feel" that is the point of the home brew type gun, and shipping is not that bad, for now. I personaly dont think a bolt that has a "ring" with a press fit then tig welded on the outer most part of the bolt head will change the temper of the luges. all three of the metalolgist at work, one of witch has a back ground in welding state that welding will change the temper but not to the point of failure. I'm not saying there word is 100% but it is the best ed. guess that I can come up with at this point in time. I welcome what you wright in this form. at this point in time a .223 ak is about progect #3 on the to do list, not in cluding the honey do list that will not stop growing on a daily rate. so I have some time to ponder on this one. as far as the spring loaded firing pin I think hcpookie has worked that one out on his .308 build.
btw have you given anny thought of using a -74 mag with a modifide follower for your .223 ak. -74 mages are cheeper and the mod. is easy to do. muttman
 
#19 ·
If you clamped a couple of copper heat sinks to the bolt I don't think the lugs would get hot enough to lose any of their temper . A few small quick tack welds is all that it would take and let it compleatly cool between welds. Silver solder should also work, solder the ring first then cut the clearance for the extracter. The base of a case is designed to take the pressure of a round. Its only when folks try to get more out a round than it was designed for or there was a mistake made that they fail. Guns that head space on the shoulder or case mouth do not always compleatly enclose a round. The 1911 is the worst culprit that comes to mind. The barrel and web in the case head are what contain the pressure. Metal used in guns is usually not all that hard, and if a part is hard it is usually more for wear resistance, and improve resistance to perminant deformation. Metal selection and heat treat is not so much about containing the pressure as it is the 10,000 times the bolt will be slammed into the lugs. Which is why excessive head spacing is bad, it gives the bolt a little room to gain some speed before it slamms the lugs.

Now I'm not a metalrgist, I'm an electrician, but I did learn a few things about metal when I was a job shop machinest, and some cool stuff about heat treating and tool steel when I was making chips in a tool and die shop.

So don't try this at home folks and I am in no way recomending anyone else try it,

when I get to the .223 project after the milled rewelds and the tabuk I'm going to tack weld a ring into a romy bolt.

hey muttman got a link for that 74 mag mod?
 
#20 ·
I would be interested in the mag mod. I am only using 10 rounders in my build as it is shot from the prone position 99% of the time. the bulgy mag was cheap enough and I only need 2. I have also seen some galil mags in shot gunnews that were priced fairly reasonably. I have seen HC,s firing pin conversion and plan on doing some thing simular on both my 308 build and a 1.5x308 build. I have been reloading using the military type hardend primers, so for now I have gotten away with out spring loaded pins on the 7.62x39 builds.
 
#21 ·
fordgalaxy and 1biggun,

the mod is to the mag falower. the link is on saiga-12 forms. the member that did the grunt work is dizang. he will make the changes for a small fee, however you could make the changes as he does state this in his post. photo #2,and3 are the modes for the saiga not sure if they are needed on a non saiga build.


http://forum.saiga-12.com/index.php?showtopic=9148

I have not made the changes yeat (still working on other build) but have not found a bad posting after the change was made. muttman
 

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