7.62 X 39 bore, .308 vs. .311, what gives?

[His lordship.]

One of the contributors a few months ago, as well as my handloading book, had noted that the Ruger Mini-Thirty and the bolt action rifles in 7.62 X 39 use a .308 groove.  And the imported rifles in this same caliber use a .311.  Wouldn't this cause a pressure problem as the contributor noted?  And why would Bill Ruger do something like that?   :?

Thanks.

[Mikey]

Chris:  Apparently reducing the size of the 7.62x39mm cartridge to .308 in the Ruger Mini-30 has little or no effect on accuracy.  I'm not certain you will find a moa mini-30 but they should group to within 2-3" at 100 yds., or maybe better if you are lucky.

Why would ruger do that - who knows, unless it was a general lack of readily available ammo at the time or suitably reloadable .310-.311 bullets, making the 7.62x39 a mini 308 would have more marketing appeal than something with a strange bore diameter.  

Howsoever, after reading a couple of articles on increased bbl wear due to the use of oversized boolets I hain't so sure I would spend the $ for a mini-30 only to put serious wear in the bbl before too long.....  Mikey.