I've burst fired enough ammo through an M16A2 fast enough to melt the handguards and cause repeated cook-offs, and that rifle still shot fine afterward. The key to buying an AR-variant, IMO, is finding one that has a chrome lined bore and chamber like the Mil-Spec rifle. If your AR doesn't have a chromed bore, then throat life would be short. Of course, it should be pointed out that SKS' and AK's have chromed barrels. It is my opinion that any semi-auto rifle that is meant to be fired more than 3 rounds in rapid succession without cooling should have a chrome-lined bore. It add a small amount to the cost of the barrel, but is tenfold worth it for this type of application. I know that Rock River Arms offers the option of chrome lined bores with their AR rifles.

Mike