I've used Rainier Arms, Spikes, PSA, LMT, BCM, DD, Young's, JP, RRA chrome, and Black Rain Ordinance.
The RA Thunderbolt HP MP C158, had cycling issues as the gas rings were damage after only a couple mags. Even with bad rings it was cycling milspec stuff, just not the underpowered russians. After a new set of rings and judicious lubing, it ran like a champ. I honestly think that I underlubed it and borked the rings.
The Spikes Tactical HP MP C158 rain like a champ no issues, but the whole Spike's upper as a whole was over gassed.
The Young's needed an o-ring to extract. After which it ran like a champ but only used it for like 100 rounds as I had it on a precision build so only shot like 100 rounds through it. (that heavy 223 ammo is expensive >.< )
The JP bolt is 9310 not Carpenter 158. Only have a couple hundred rounds through so I can't say too much, but the LMOS system is effin incredible. 9310 is supposedly more expensive and tougher than C158. I honestly want to put them in ALL my ARS. But GD they are expensive.
The RRA Chrome haven't had a issue in the 3+ years I've had it and lauched thousands of rounds through it. Its my only semi auto carrier, I don't know the specs. It's still bright shiny and pretty. But it cost me alot more than my standard milspec MP HP C158. Would I buy another one? Naw, I'd rather have a PSA Premium and 10 boxes of ammo, thank you.
The BCM LMT DD PSA all HP MP C158 no issues with prolly over 1k round through each.
The Black Rain Ordinance Nickel Boron had what I believe was an out of spec firing pin issue. Too many failure to fires to adequately formulate an opinion.
Honestly, the carrier doesn't really matter (except the lightweight LMOS). The coatings don't matter. Only the Bolt assembly matters.
IIRC only the LMT and BCM came in brand new, but dirty, just like it should be if it was individually tested. This is not to say that ther others touting HP MP testing weren't individually tested, then maybe cleaned. But more likely they are only batch tested.
The only difference between a good bolt and a bad bolt, is how long they are gonna last before a stoppage. If you are going to use your rifle in a way that a stoppage could mean the difference between life and death, I'd put my money into a HP MP C158 bolt, if only for peace of mind.
But I'm really loving this LMOS system.