303 Bullets Used in the 7.62x39 for Subsonic Loads

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tkcomer

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Kinda long, but here goes. I have a friend that was bent on getting a 300 Whisper upper for his AR. He wants to to put a can on it and go subsonic. Until he saw my upper in 7.62x39. Then he got the idea of getting a 7.62 upper with a .308 barrel and using that case for his subsonic rounds and have a full power gun to boot. Trouble is, we cant find a barrel for an AR in .308 with a 7.62x39 chamber. Now he's thinking of getting a .310 barrel and shooting the heavier .311 (303) bullets for the subsonic loads out of it and still be able to shoot standard .310 bullets for full power loads. Kind of a dual purpose gun. He's heard the pros and cons of shooting .308 bullets through the .310 barrel and will try that as he loads for 308, but wants to know has anyone tried using the .311 bullets through the .310 barrel for accuracy. I know this is an unusual question, but I hope someone here has some answers. I'll not even get into what powders to use for this combo. Thanks for any advice on this.
 
I've tinkered around loading a 150 grain Hornady .312 bullet (intended for 303 Brit)...

These are for my converted Saiga, which slugs at .312 at the muzzle.

I loaded them with 1680 and they shot o.k .... no signs of overpressure .... but didn't group for beans....

I hope to tinker with the load and see if I can work up something that performs better.

I can't seat the bullet at the canalure, as it has a very gradual sloping ogive.

So I seat at max OAL for the magazine and the neck tension from stuffing the .312 bullet seems to be all that is needed to prevent set back.

If your interested, I can dig out my notes and tell ya what didn't work.
 
A .310 barrel will shoot .308 bullets just as well as it will .311 diameter projectiles
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Unless it's an AR; the gas system doesn't seem to like the 308 boolits so well.

I use Hornady 174gr RN .311/.312 bullets for my thumper 7.62x39 loads. I can get them up to 1900fps, but I suspect that they'd do just fine in a subsonic load. They run thru my .3105 barrel just fine.
 
Unless it's an AR; the gas system doesn't seem to like the 308 boolits so well.
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Sounds like your rifle or loads need more tuning, I have no such problems shooting .308 bullets in my 20" A2 in 7.62x39 in fact I have yet to shoot anything other than .308 bullets for my AR15 7.62x39 handloads. If your rifle won't run on .308 bullets there's something either wrong with the rifle or the load.

My equivalent load is a 170grn Sierra flat point loaded to 2000fps accuracy is great especially for a non freefloated AR, 1.5 to 2moa 5 shot 100yd groups. Plus they are much cheaper than their .311 diameter counterpart. Thus far I have yet to have any feeding or function issues with .308 bullets
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Perhaps your friend is unnecessarily worried about accuracy

I know you are very aware, but subsonic is 1125 feet per second in dry air. But to eliminate the crack of supersonic flight you need to be Mach 0.9 or less. So that's 1012 fps or lower. Even with a heavy bullet, once you achieve 1012 fps or less you will find that accuracy is very elusive. Or maybe it even sucks, when your bullet doesn't match the bore.

Cowboy rifles often shoot subsonic and get tolerable accuracy, but their bullets are made for the gun. Your friend certainly should not expect match grade performance. Loosen up your expectations. I know you'll achieve your goal, but don't expect to have a match rifle.

Get the standard bore for 7.62x39 and try both .311 and .308 bullets. If they don't work, you can always get .310 and be happy with it.
 
One final comment:

So your friend wants to buy a 7.62 upper for $475 plus shipping, then a suppressor for about $795 (and isn't there a $200 tax stamp?) but then he want to get cheap about the bullets? Baloney.

Buy Hornady .3105" bullets in 174 grain for the 7.7 Japanese rifle. Those will work perfectly in your 7.62 upper.
 
This setup won't be cheap if he does go through with the plans for a can. Neither of us are sure how the .308 bullets will behave in a .310 barrel in subsonic loads. Especially in a gas gun like the AR. My idea is to get a gas block that you can turn off as the gun probably won't cycle with these loads. No sense damaging the brass due to a short stroking gun. Spotted an article that says if you use 180 or 200grn bullets you can use 44 mag pistol data. The plan is to get the barrel and then start in on load development. If it works out, then start jumping hoops to get the can. The guy loads for his .308 bolt gun so he has a few bullets to try. I don't think he has any of the heavy weight ones though. He is going to try .308 first, but wanted to know about the .311/.312 bullets in case the .308 didn't pan out.
 
If I was really wanting to go subsonic I would do a whisper. The main problem I have seen is some of the people doing the whispers don't put a fast enough twist to stabilize the 220+ grain bullets.
 
I think you need a 1-8 for a 240 grain in a whisper. A 1-10 would work for any .312 bullet unless you got some custom mold made with a super heavy slug. The heviest bullet for a 312 range that I know of is a 215 grain Woodleigh
 
What I was really looking for was a less powerful FUN round for the SKS. Kind of the 30 carbine or 32-20. Cycling the action was not a factor, one could do so manually very rapidly on reduced loads and pocket the spent brass with no loss or dings. The cast 150 grain .311 worked good, but since I had a box of 500 cast .312 125 grainers for my 32-20--you know the rest of the story! Pockets drilled out to .125, regular primer and six grains of Unique. Popping cans at over 100 yards was not a problem. Fast and accurate with minimal recoil. Works faster than a bolt action!
ROD
 
This thread was two and a half years ago.

Be mindful that half the guys on this thread aren't on this Forum any more.
 
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