7.62X39 to .308 Adapter Worries?
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Thread: 7.62X39 to .308 Adapter Worries?

  1. #1
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    Default 7.62X39 to .308 Adapter Worries?

    I just bought a neat little chamber adapter that lets me shoot 7.62X39 in a .308 by basically filling the chamber with a .308 cartridge-sized hollow adapter that holds a Russian cartridge inside it. (I use such an adapter to shoot .45 LC in my Martini-Henry "Zulu" rifle, a cheap solution to very expensive and rare ammo.)
    The Russian bullet in the .308 adapter travels a short distance unrestricted through a smooth and loose section of the adapter before entering the throat's rifling. .
    Joop brought up an interesting and very relevant thought on such an adapter -that it might possibly lead to damage to the throat of the rifle using the adapter.
    I've been wondering if this might happen. It seems it is possible for two reasons, but I'm not sure whether it would really be a problem:
    1) Hot gases might leak past the bullet base as it is fired and going through the loose straight section, burning the throat more than they would do if behind the bullet. Are hot gases more destructive to the throat in this situation than if they hit a microsecond later behind the bullet normally? Doesn't seem like it, but maybe.
    2) The bullet might enter the throat angled or off center a bit from free travel before hitting the throat, resulting in uneven pressure and wear. In this scenario the FMJ bullet from the Russian round is slightly skewed and sort or rattles into the throat, seemingly very possible.

    The second scenario seems more likely to damage things than the first to me, but it is perhaps no more dangerous to the barrel than using shorter bullets in the regular .308 chambering that don't reach all the way to the throat, like soft-points. It used to be that for maximum accuracy it was believed a bullet had to be pushed right up against the throat, but I think that belief may have been discarded, meaning lots of bullets come rattling up to the throat a bit loose.

    As I very much value Joop's wondering about the possibility of barrel erosaion or wear and don't know an answer, any thoughts from other members? I haven't tried the adapter yet.

    .

  2. #2
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    I bought a handful of cartridge conversions from a company called Ptarmigan. I've never tried them. Unless you have at least a half dozen, it is such a slow process...it would seem.

  3. #3
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    On top of your concerns 7.62x39 is usually loaded with a .310 diameter bullet and you are tring to force it through your 308 bore. I don't think I would do that.

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  5. #4
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    Quote Originally Posted by groovy mike View Post
    On top of your concerns 7.62x39 is usually loaded with a .310 diameter bullet and you are tring to force it through your 308 bore. I don't think I would do that.
    This was my biggest concern. To add to that, most commercial 7.62x39 ammo has a bi-metal jacket (steel) that will likely only expedite the problem (not as big of an issue as most US rifle snobs would like people to think, but when you start pushing it through a bore that's smaller than what it was designed for, I can see it being a possible factor).

    John

    ETA: I forgot to ask; Do you handload? You could use 110 grain .308 bullets with a mild charge or, if you're loading for Mosins, use the smaller 124 grain projectiles made for x39, using the same theory. And, if you load them hotter, they're super fast and accurate, as well.

  6. #5
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    Quote Originally Posted by groovy mike View Post
    On top of your concerns 7.62x39 is usually loaded with a .310 diameter bullet and you are tring to force it through your 308 bore. I don't think I would do that.
    2 thousandths of an inch is nothing to sweat over. Most people don't realize how small that is, it's probably within the tolerance of the barrel diameter for most surplus military rifles.

  7. #6
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    Quote Originally Posted by izzytok46 View Post
    2 thousandths of an inch is nothing to sweat over. Most people don't realize how small that is, it's probably within the tolerance of the barrel diameter for most surplus military rifles.
    agreed but we dont know if it is being used in a military rifle. and just because it is "probably" all right doesn't mean its a good idea!

  8. #7
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    I bought one from a guy in Alaska, I installed it in a Spanish 1916 rifle in 308 and only shot 100 rounds thru it and didn"t have any issues with it. I liked it.

  9. #8
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    That's who I bought from - I don't handload currently, but may have to take it up again.

    Quote Originally Posted by bsd View Post
    I bought one from a guy in Alaska, I installed it in a Spanish 1916 rifle in 308 and only shot 100 rounds thru it and didn"t have any issues with it. I liked it.

  10. #9
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    Is that guy still in business or did you get the adapter sometime ago? I could use one of those 7.62x39 adapters for my Spanish 1916.
    Damn the expense, use your turn signals today... and as a special favour, try doing it before you have two wheels in the next lane.

  11. #10
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    I just got it. Quick delivery. The adapter is temporarily glued into the chamber with Loc-Tite.
    Here's his link:

    http://www.mcace.com/adapters.htm

  12. #11
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    AHA! Good news. I emailed them ages ago and got no reply so I thought they had gone under even though the site is still up.
    Damn the expense, use your turn signals today... and as a special favour, try doing it before you have two wheels in the next lane.

  13. #12
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    I wouldn't give it a second thought when "downsizing' with adapters. Check your bolt face for obvious signs of blow by, but I don't thin you'll have any problem.

  14. #13
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    I have a Ruger Mini-30 and a Model 77 bolt action in 7.62x39. I understand that Ruger has designed a short section of the barrel in front of the chamber to act as a swage to reduce .309 - .312 diameter bullets down to .308 diameter before they enter the rifled barrel. The adapters should work OK except the bullet "jump" in the adapter might cause accuracy to be less than desired.

    I also reload 170 to 190 grain lead bullets in my .308 Win cases to about 1800FPS and seat them out far enough to be lightly engraved by the rifling. This has improved accuracy by eliminating bullet jump. This is not recommended for jacketed bullets because it can increase the pressure peak before the hard bullet can start moving down the barrel.

  15. #14
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    I cannot see how any blow-by from a loose fitting chamber adapter could affect the throat in any way. I'd not worry about that one at all.
    I don't see how running a lower pressure, lower volume cartridge in a rifle intended for a much hotter round could affect the throat in any way. No worry there either.
    Since you have to pull the adapter out of the chamber to reload it is unlikely you'll get it back in the same way it came out, as far as rotational orientation. So for that reason the chances of wearing out the throat of the barrel due to offset bullets is really down there. I'd not worry about that one either.
    Running 310 to 313 diameter bullets in your .308 bore isn't a worry especially since you're running a lower pressure lower volume cartridge. Even if you jack the pressure up 10% which is very unlikely, the area of the cartridge is much lower so the gasses acting on it have less effect. This means the load on the bolt due to bolt thrust will be less than a standard 308 round and therefore not a problem.
    Last one is the silly and unfounded idea that the copper plated steel jacketed bullets in the russian ammo is going to wear your barrel out faster. The real wear is caused much more by heat than by the bullets. Since you'll be lucky to fire one round per minute when changing out the insert its a low probability that you're going to overheat your barrel and cause much wear. Since everyone refers to the luckygunner test as a biblical Canon of truth I'd suggest someone try doing a real comparison test using the same powder and bullets before deciding the bullets are the issue. It would also be nice to see a 10,000 rd test where they didn't overheat the crap out of the rifles trying to get all the testing done in one afternoon. That creates a lot more wear than any type of bullet used.

    So the basic answer to your questions is yes you can run the chamber insert without worrying about causing more wear on either the bolt, barrel throat or bore.

    Good luck
    Frank

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