I'm not much of an AR zealot like many folks here seem to be. I've had experience only with Colt ARs, and only three of them. No complaints. I seldom do any modifying to any gun - no trigger or handguard replacements, no optical sights that have oddball reticles or require batteries. If a firearm doesn't perform as expected straight out-of-the-box, I generally don't keep it long.

I can't see a need to overheat or abuse a barrel by seeing how fast a magazine can be emptied. To me, ten rounds through an AR means it needs a cooldown. I've tried many cheap, bulk ammos - all went bang but none were accurate. The only factory ammo I've found that shot with good accuracy was a Federal Match round. Lots of experimentation with powder, bullets and primers has resulted in accurate handloads.

After reading the comments on this thread, it seems it might be worth the trouble and expense to buy one or two AR copies, maybe an S&W and/or Ruger and do a lot of shooting. I have no real idea what is available from either manufacturer or others. I don't know whether buying the cheapest model, the most expensive, or somewhere in between (if such choices are available) would be the best route to follow, but it might serve as the basis for an interesting informal project.