"Which 308 platform should I get into?" is a big question on folks' minds.
At present, this article is a dumping ground for miscellaneous facts, which I hope to whip into a real article down the road.
Like the AR-15, the AR-10 is a direct gas impingement system.
The PTR-91 is, like most HK weapons, a recoil-operated delayed roller locking system system. Like the HK91, the PTR-91 uses a fluted chamber to improve extraction reliability. This is at the cost of doing much greater damage to brass than any of the other 308 rifles mentioned here.
The PTR-91 / HK91 rifles accept the ubiquitous G3 20rd magazines. At present, they're available for around $2 apiece.
M1A's accept M14 magazines or M1A magazines.
AR-10s have their own type of magazine.
Ease of Maintenance
The AR-10 and SR-25 are both related to the AR-15 platform, and as a result are very easy to open up and service.
The PTR-91 is, like most HK-pattern weapons up untl the late 90s, welded together. While getting the bolt out is fairly easy, stripping it down completely is far more involved than in the AR platform.
-- SeanNewton - 02 Jan 2009