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Last edited by JC5188; 07-01-16 at 05:19.
All other factors being equal, there is likely some analogy to the varying degree of frictional parts wear of engines where the intake of airborne abrasives differs.
Two engines, same hours, one with high-perfomance, multi-stage air filtration, and another engine with a simple, economy air filter. In this case, one of these engines will injest more silica (abrasive dirt) and this will translate into much more upper cylinder wear. Think of what a hole in an air intake hose between the filter and the intake manifold can do to drastically increase top end and bottom end wear as that engine turns into a sand pump.
Or same engines, same filtration, sames hours of operation, but one runs in an environment where it is subject to greatly more airborne silica. That engine will simply show more wear on its internal components over time.
In the situation of these rifles, obviously without filtration of any kind, they are more like little engines with splash lubrication and no oil filters. Leaving the abrasive-contaminated lube oil in place to continue to circulate means increased wear, and therefore lube oil changes and the removal of silica-contaminated oil directly equates to less wear and longer component life.
If there is greater wear on the cam pin actuator in the upper, will this translate to greater stress in unlocking the bolt, specifically on the bolts lugs?
Colt must have seen some sort of issue to go to the trouble of adding the little steel plate at that point in many of their newer uppers.
"Addressing the problem of shootings by ban or confiscation of non-criminal's guns is like addressing the problem of rape by chopping off the Johnson of everyone who DIDN't rape anyone while not only leaving the rapists' equipment intact, but giving them free viagra to boot." --Me
I shoot till something breaks. I'd rather spend time shooting or reloading vs getting all anal about measuring wear.
While perhaps an interesting academic exercise there are pretty much no universal truths.
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.
Last edited by Cincinnatus; 07-03-16 at 15:31.
"Addressing the problem of shootings by ban or confiscation of non-criminal's guns is like addressing the problem of rape by chopping off the Johnson of everyone who DIDN't rape anyone while not only leaving the rapists' equipment intact, but giving them free viagra to boot." --Me
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