Any long arm is legal to sell and possess in MA as long as it meets the criteria for the MA AWB. That means no flash suppressor, not bayo lug, no new hi-cap mags. If I were to buy a new 308 semi right now, it would an M1A, as you USGI, pre-ban hi-cap mags can be had with minimal effort.
Actually, the AWB is a little more specific. The definition:
Semi-automatic rifles able to accept detachable magazines and two or more of the following:
- Folding or telescoping stock
- Conspicuous pistol grip
- Bayonet mount
- Flash suppressor, or threaded barrel designed to accommodate one
- Grenade launcher
Semi-automatic pistols with detachable magazines and two or more of the following:
- Magazine that attaches outside the pistol grip
- Threaded barrel to attach barrel extender, flash suppressor, handgrip, or silencer
- Barrel shroud that can be used as a hand-hold
- Unloaded weight of 50 oz or more
- A semi-automatic version of an automatic firearm
Semi-automatic shotguns with two or more of the following:
Folding or telescoping stock
- Pistol grip
- Fixed capacity of more than 5 rounds
- Detachable magazine
So, by definition you CAN have a rifle with a flash suppressor or bayonet lug, but not both - there have to be a least two of the "evil characteristics" present for it to be a so-called assault weapon. Also, if it was manufactured before the ban went into effect, it is good to go.