The SAK marked barrels are standard contour USGI chrome-moly NM barrels. They are not chrome lined. IIRC, SAK also made some medium weight barrels in the 80's, but I think those are marked with General Dynamics cage code as Saco-Lowell had been bought out by GD by then.
TRW made both chrome-lined barrels & chrome-moly NM barrels.
Both the SAK & TRW NM barrels are very nice, the problem is finding one in new condition.
EDIT: Oh crap, I r dum. As Jeremy said, they did make both. Sorry for the error. Pretty sure they did make the medium weight barrels in the 80's though.