I bought an AP4 in 2007 and it's run just fine. So far only put mil-surp and handloads through it. It'll shoot 1" groups from a bench with my handloads, but with mil-surp it opens up to 2-3, except for, believe it or not, some NATO spec stuff that came from India, which it loves. Green sealed primers.
My typical handload for it is 42gr of 748 under a 175gr Sierra HPBT. These are the bullets we loaded in the Marines for our M21s in the mid 80s. I also have some of the 168s, but my M1A prefers the 175s so I'm just sticking with them. They are also mil-surp.
I've done a few range sessions with the AP4 that were geared towards 'breaking it'. Not in a real torture test, mind you - as mil-surp is too expensive for me to do that now, and mass quantities of bullets/powder/primer for reloading can be tough to come by occasionally lately. But those sessions, three or four of them, were each around 500 rounds, the first 200 being all rapid fire as quickly as I could change out my magazines. Never had any kind of problem during these, save that barrel heated up a good bit.
Never fired a RR.