If figures the newbie has a dumb question for the board.  Ok here it is.  A guy wants to sell me an upper.  It is a 16 inch heavy barrel with 310 printed just in front of the front sight. It also has an A in the shape of a triangle in front of the shell deflector.  I never assumed it was anything but .223.  I put it on my lower to function check it and it worked fine.  Loaded the mag and attempted to chamber a round, bolt would not close and it pushed the bullet into the casing. Disassembled it and examined it. The bolt face is larger than that of a .223 and the bore is obviously larger than .223.  The rocket scientist advised he was not sure what caliber it is.  It is a nice upper for what I believe is a decent price.  Any one have a clue what I am dealing with.  Possibly 7.62 X 39?  

Oly Arms (OAI) stamps the barrels of their 7.62X39 uppers ".310", that's the bore diameter.

Alright the newbie has been educated!  Next question before I buy this thing.  Where can I get mags to fit my RRA lower that will hold 7.62 X .39 ammo and how much will they cost?

Equipment Exchange

Look at the top right side of this page, just under the flashing banner.  Click the EE lettering, then look in AR-15 mags.

P.S. Considering on how old the upper is, Tweak himself may have built your upper when he worked for them.

Well, standard 223 mags will work IF you only load less then 10 rounds, so they say.  After that, the taper on the cases bind up the rounds.  At least you can go play then...

Price for 7.62x39 AR mags.... ranges from 25.00-60.00 depending.  The "ONLY" ones that work are "hybrid" mags... they have an AR top w/ an AK bottom.  They have been called Frankenmags...  USA mags made some and actually (GASP) work!

Current 7.62x39 Ar uppers are going about 450-550, depending on config...FYI.

Nah, I built very few .310 uppers. Did a lot of Simunitions tho.

Batman,

Make sure that the ejector has an extra large radius on the end of it and that the rear of the bolt is shorter than standard. If it's a kit gun that may not have been done.

Thanks for the quick and accurate responses.  This board never ceases to impress me.  It looks like I am going to invest in a 7.62 X 39 upper.