Alaman...
You've got 2 main ways to go for hicap semiautos... question on your M1A1 - is that a Garand or an M14 (M1A is semiauto M14)? If you do have a Garand, you'd enjoy the M1A/M14 type rifles' similar operational details. M1A/m14 hicap mags are expensive, though.
[And if you have an M1A/M14 you might like a Garand, though good Garands are hard to find, are not hicap, don't have chrome-lined barrels.]
Sooo....
1) AR10 from Armalite or Eagle, in .308. Get a chrome-lined barrel (not a cheaper Eagle unlined barrel, nor a "match" barrel). If you can order an Eagle you'll save a few $$ but special order the Armalite chrome lined bbl. Advantages: drill, features, and a few parts interchange with AR15. Quite accurate when using quality surplus ammo (Radway Green, South African) or Fed GMM. Nice trigger for out-of-box AR-type rifle. Disadvantages: 20" A2 flavor is heavy. Hicap mags can be a bit expensive (M1A conversions). A bit pricey - at least $995 for the Eagle.
2) FAL clone: build up (or have it done for you)
a parts kit into a postban FAL. Recommend metric FALs due to plentiful parts supply. Wonderful rifles, parts are cheap. Getting a new barrel will essentially give you a new gun (maybe replace gas piston & cylinder too). Round up the appropriate count of US-made parts to keep it legal under Sec. 922. If you're building up a FAL kit, start with an Imbel or DSA (DS Arms) receiver as they're known to be in-spec. Stay away from Century Arms mishmash parts guns. Advantage: cheap (if you start basic), great rifle, parts easy to get, US parts are getting more plentiful. Surplus hicap mags are cheap!! Disadvantage: short supply of new chrome-lined milspec bbls, heavy trigger, only reasonably accurate (certainly good enough for combat duty).
See http://www.arizonaresponsesystems.com
Unless you are buying an HK91 (G3 derivative) I'd stay away from the HK clone kits. Looks like lotsa flaky stuff to me. Building requires some welding on to upper receiver. Real true HK HK91s are pricey animals and mags are expensive but they're great. [They do have fluted chambers and are thus hell on brass, resultant brass not really suited for reloads.] Hicap mags are also expensive.
Bill Wiese
San Mateo, CA