"...it's a "squeeze bore" gun..." No, it isn't. There's no such thing. You have an early Mini-30(inaccurate and over priced) made before 7.62 x 39 ammo was easy to come by and cheap, Stateside.
.308 leftover barrels from abandoned Ruger XGI project were used to manufacture Mini 30:s until approximately 1994. I'm not quite sure what you'd like to call the tapered throat that was machined to mate .311 7.62x39 chamber to the .308 bore, but "squeeze bore" is just one of the common terms used to describe the feature. Additionally, I wasn't aware that $320 for a pristine Mini 30 with a Hakko scope and a bunch of accessories, magazines etc. was overpriced. The scope alone sells for more than that so in essence this is a "free" rifle.
Inaccuracy, as a possibility because I haven't even fired it yet, is the reason for why this thread exists. Gauging the possibilities beforehand is often a good idea and, out of sheer curiosity, I wanted to know what practical limits of lapping a barrel might be. Mission accomplished, thanks to everyone for their input.