Thinking about getting a YHM 7.62x39 upper. Does anyone know if the bore is set up for .308 or .311 bullets? I know the Euro ammo is .311 and I measured some bullets from some U.S. stuff and they are .308. Savage won't tell me their bore diameter, CZ says .311, and I think but don't quote me, Ruger is .308. Can someone with some understanding of all this tell me what most AR uppers are set up for. I would ask for bore diameter but it gets too confusing with some people talking groove, some lands, and some bullet diameters. Just like to know the current mfg specs on their bores.

thanks,
BM

Get a gunsmithing book and slug your bore. That is the ONLY way to know how big the hole is. Both 308 and 311 jacketed bullets are made, so it's really no issue IF you know the bore size and the bullet diameter.

BTW this issue is not confined to 7.62x39s. I've slugged both US Krags and SMLEs that went as low as .306 and as high as .317.

Yah, in Europe they go by the bore size, which is to say, across the lands (the high points), where here we go by the groove diameter (the low points).

So here .308: bore would be .300 and groove .308.
Over there 7.62 (here it's .308), is measured across the lands =.308, so the bore 0.312".

Best to go Euro if you buy surplus or Euro ammo. I have a Finnish Russian capture Sako re-barreled m91 that has a true .308 groove and .300 bore. If I were to try shooting Euro 7.62x54R I'd be in big trouble as pressures would soar off the charts; their bullets being 0.312" diameter.

It is very likely .308, and the surplus ammo is going to be .311, whcih may or may not cause an issue.


IOW...clear as mud!

Sorry but you are incorrect, it has nothing to do with Europe vs America.

There are rifles out there (AK47s for example) that are made for Russian ammo that uses a .311 bullet. There are others (Mini 14s for example) that are made for .308 bullets as are loaded in WRA factory ammo.

SLUG THE BORE !

A call or email to YHM should resolve the question for you. I'd guess if it is chambered for x39 it will be .310, but I'd want to make sure before I fired any in it. I have an Oly upper and .310 is stamped into the bbl right in front of the gas block. Lots of fun to shoot and much more accurate than I expected with the crappie cheapo rusky ammo, I have high hopes for doing some handloads in it. CH

"A call or email to YHM should resolve the question for you."

That would be too easy !

Russian, eastern european coutries of former Warsow pact, chinese Ak47, VZ58, AKM, SVD Dragunov, Mosin Nagant, SKS, etc had and have .310 to .312 barrel.
The finnish Mosin Nagan normally use .308 to .309 barrel, the finn made the distinction of the 2 cartridges: they call their 7,62x53R instead of 7,62x54R but they digest both in case of need most of time.
The 303 British and 7,7 Jap have very close if not same size as the original russian barrels.

US made 7,62x39 barrels (AR and Mini) are generaly .308.

It's why dies makers equip their reloading tools for such calibers with 2 sizing olives.

I had for two years a AR15 in this caliber that digested russian and czeck ammo without a blurp or over pressure and functionned flawlessly.

Dom

cast .309 and run with it.

Call YHM and find out.
Make sure you get a 308 barrel. WAY more bullets to choose from with the chance you'll actually find a good one. Forget the surplus, ever since the Chinese steel core and E German ubungs plastic went away, I haven't found anything worth beans from the surplus market.