When buying a newer manufacture M1A make sure you get one with an F code bolt.
From the July 03, 2007 draft of the Third Edition of M14 Rifle History and Development:
Bolt - Springfield Armory, Inc. M1A bolts are manufactured in the United States of America. The M1A bolts are typically marked 7790186-SA on the first line and A00030, B00048 or F00059 or similar number on the second line. They may have markings such as D and M3 on the rear end and A9 or B1 on the bottom surface. The letter A prefix for the number under 7790186-SA means the bolt was cast then finish machined. The letter B prefix for the number under 7790186-SA means the bolt was machined from bar stock. The letter F prefix for the number under 7790186-SA means the bolt is forged. Springfield Armory, Inc. began installing F prefix M1A bolts by no later than 2000.
When I look at buying an M1A, I make damn sure it either has an F code bolt or a real GI one, you do not want an A code bolt! These rifles cost alot of money for a cast receiver copy so be careful what you're buying.