Quote Originally Posted by ace4059 View Post
I do not think the wear on the cam pin actuator in the upper is great at judging the round count of an AR-15.
I say this because I just looked at four of my uppers that vary in round count. Mind you, the uppers that I just glanced at are dirty and have not been cleaned for some time. I just pulled the BCG out and used a flashlight to do a quick glance.

Here were my observations;
SPR with a 20" barrel with rifle gas system, rifle buffer setup. Im on my 8th box of 1000 rd of Nosler 77gr CC but I still have quite a few of this last box loaded. best guesstimate is 7,200-7,300 rounds. It has minimal wear on the upper cam area. Only polished areas where the anodizing has worn to smooth aluminum. The BCG has the finish on the rails worn off and its "polished smooth". Only shot suppressed with 77 gr MK262 clone ammo. I would have guessed this one would have the most wear because the BCG becomes sluggish after 100-120 rounds suppressed so I have to give it an oil bath every 80-100 rounds.

14.5 SBR BCM 556 upper midlength gas with h3 buffer. Only shot suppressed. It has almost 6,000 rounds down it and has minimal metal removed from the wear on the cam pin actuator in the upper. Its more than just polished, it does have aluminum removed. 556 ammo only. probably a little less metal removed than the OP's pic.


9.5" AAC 300 blk upper on A5 setup. Only shot suppressed with 125gr hunting loads. No subsonic ammo. This gun is used for hunting only since the ammo is expensive and has MAXIMUM 600 rounds through it including load development, sighting in, and hunting. Its common for 10-30 rounds per hog hunt. It has a lot of wear on the cam pin actuator in the upper. This has metal gouged out of the upper and I had to replace the bolt and cam pin because it was binding in the upper and causing the BCG to stick. I tried the bolt and cam pin in another upper and it worked correctly. It has a small "rail" gouged or worn in the upper from the cam pin. I probably need to file it smooth.

11.5" bcm 556. This is a lesser shot SBR of mine. I liked it when it was new but it has lots of muzzle blast and it sits in the back of the safe now. Ive tested in on several different lowers and it is mainly shot un suppressed. It has maybe 1,200 rounds through it probably closer to 1,000 rds. It defiantly has less wear than the AAC upper, but has a lot more than the 14.5" upper. I shot all sorts of ammo through it from steel cased to MK262.

Im not sure what all this says about wear but there maybe several factors. I think the DI gas length plays a part, but the buffer setup might also. But then it could be the tolerances of the manufacturing process between the cam pin and upper... who knows.
That wear pattern is not unheard of. The use of the A5H2 in 300 Blackout can work well in all 4 functions for that said buffer mass more than 5.56 for SBR comparisons. Generally, an A5H3 or A5H4 may suit a user better for suppressed supersonic operation in an AAC 9", just depends on the attributes of that can and ammo.