.308 to 7.62x39 caliber conversion

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KotKotofeich
Posts: 8
Joined: Wed Mar 13, 2013 2:52 pm

.308 to 7.62x39 caliber conversion

Post by KotKotofeich » Wed Oct 02, 2013 2:03 pm

This is a question that has been asked several times but never answered conclusively and in detail:

Caliber conversion from .308 to 7.62x39, what would be involved? Can the conversion be made reversible? I'll try working from that assumption...

New barrel. Can anyone say if there are any type of AK barrels that are threaded into the trunnion like valmets and use the same thread (26x1.5 mm)? Is gas port location the same? Otherwise, manufacturing a whole new barrel is an option.

Gas block. Is an AK gas block the same dimensions? i.e. would a valmet gas tube match on to it? Ideally I would like the end result be two barrels with gas blocks that can be switched as needed.

Bolt. Never having seen a 7.62x39 bolt/bolt carrier (only have a .308 and .223) can I simply replace the bolt? Bolt carrier and bolt?

Magwell. I'm pretty good with CAD, I'm hoping I can design and 3d print an insert to make the magwell take the 7.62x39 magazines. Or can it still feed from .308 magazines?

Anything else I'm missing?

If it's doable at all, I'd like to try it. The important part is to make it reversible so that no Valmets are hurt in the production of this movie.

Someone might say that it's easier to get a 7.62x39 rifle to begin with... Well, I'm in Canada - anyone want to trade? ;)

bruh44
Posts: 16
Joined: Tue Aug 13, 2013 3:16 pm
Location: Middle of the desert, NV

Post by bruh44 » Sun Oct 06, 2013 12:56 pm

I'm waiting for a FA transfer of a M78 that was a 308 converted to 7.62X39 by Hard Times Armory so it can be done. I'm learning more about the gun as I go. I'm still not sure what barrel is in it, but the bolt is a standard AK bolt. Really thats for the better since Valmet parts are very hard to get. I would guess that also means the carrier is a standard AK carrier not Valmet. I put a post up about it a while back: http://www.valmet.org/forum/viewtopic.php?t=3455

These pictures may help. Unfortunately the NFA branch is taking their sweet time these days and are telling me my transfer won't be complete until April 2014. Now that there's a shutdown it's probably getting bumped to 2023.

KotKotofeich
Posts: 8
Joined: Wed Mar 13, 2013 2:52 pm

Post by KotKotofeich » Sun Oct 06, 2013 5:07 pm

Thank you, I'm going to keep an eye on your topic.

I've been doing more research since I've posted this question and it does appear that the bolt can be taken from an AK or a Galil with no problems and keep the original bolt carrier. The question that interests me about your conversion is that it seems they kept the original piston... Does that mean they changed the spring? Or is the AK system sufficiently overgassed by design that even using a weaker cartridge lets it still cycle with the same spring/gas block/piston?

From what I can see in your pictures, you have a new barrel that was headspaced further into the lower to make up for a shorter 7.62x39 bolt.

Do you know if the barrel is chromed or simply stainless - I really don't know of anyone who could manufacture a chromed barrel nowadays..

It appears that the magwell is welded at the front which serves as the new magazine support... I'm pretty sure I can make a removable insert now.

So it looks like that if I want to try it, my major outlay is going to be a barrel, but since it's threaded into the trunnion, the conversion is going to be reversible even without a press. Like I said, my goal is to make this a reversible conversion.

Guess I'll try it at some point - now I just need to find a gas block for an M-78... After that a bolt and a magazine will be simple.

Any and all input/advice anyone would have here is most welcome of course :)

bruh44
Posts: 16
Joined: Tue Aug 13, 2013 3:16 pm
Location: Middle of the desert, NV

Post by bruh44 » Mon Oct 07, 2013 2:28 pm

The dealer who has it right now told me it had gas issues because of the conversion but it is running now. I would guess it would need more gas to function with the smaller round.

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