my early AR was a Colt and the firing pin was not shrouded by the carrier, so the rim got beat up, now I use M16 carriers...
my good friend developed the SOCOM bolt upgrade, with high temp O ring to help the extractor, high temp ejector spring, and McFarland style continuous gas ring... I added the kit to my AR before my first big time 3 gun match in 1995 (North Carolina Tactical at Ft Bragg) at the end the the next year, I dis assembled the bolt, and found that the extractor spring had vanished, but was still operational with the O ring... the continuous ring was replaced with standard 3 ring set as I was shooting cheap Russian ammo for local matches, and it carboned the ring to the point of failure
a friend has a Class 3 M16, and doing a mag dump with a 7.5" barrel melted the gas tube (not sure of its pedigree), but I replaced it and roll pinned the gas block for him
not had a problem with 5.56 firing pins, but had a 9mm spring break at about 400 rounds... I rounded the strike end (as is the 5.56 pin) of an OEM Colt pin, so that the hammer strikes it closer to the center line and has over 7000 rounds in a couple of PCCs without a problem
minor gas cutting on the bolt face from leaking primers, but overall never really had a problem with a 5.56 ... the 9mm guns, on the other hand, have a different learning curve
one match embarrassment... assembled the bolt with the firing pin flange behind the cotter pin....
Les