Is it possible to ream the chamber of the Mini-30 to a more powerful .308 cartridge? I Know that the magazine length and head diameter are the limiting factors so I was specifically thinking in terms of a 7.62x39 improved for possibly 200 or so more fps. Anyone ever heard of this being attempted?
Since the external barrel diameter is determined by maximum weight and internal one by the bullet caliber, what could they do differently?
Mini-14 is as inaccurate as Mini-30 even though the barrel is supposedly designed for .223 round.
Once you have a loose construction and light barrel, you lose accuracy. Even M1A or Remington 700 which is a base for bolt sniper rifles benefit enormously from after-market accurising.
Mini-30 is considered inaccurate because it is considered for hunting and people compare it with the guns shooting 1/2 MOA. Mini-30 is in the same accuracy category as AK or SKS.
Mini-14 is never considered for hunting (with original barrel) and 4" at 100 yards is good enough for a military rifle that will shoot after a mud bath.
Apparently recent Mini-30 are .311, not .308 barrel. Also, some people have better results with .311 in .308 barrel - especially once the barrel warms up.
It's very individual.
Also, SKS is a big rifle - around 10 pounds or more. It's not an assault rifle by design or any stretch of imagination. Everything else being equal it should shoot better than a 6-pound rifle with a tinfoil barrel.