These rifles were made for Lipsey's, one of Ruger's biggest distributors. There have been a whole series of these stainles/walnut Lipdey specials.
The 7.62x39 was, I believe the second one in 2006(?) Others have included 35 Whelen, 6.5x55, 257 Roberts, 30-30, 250 Sav. and maybe others I have forgotten.
I have never measured the bore of my #1 7.62x39, but I would guess that Ruger used .308 barrels that they would have on hand for other 30 caliber rifles. The best way to know for sure is to slug it.
