I finally made it to the range to put some rounds through the .458 and I have a few thoughts on the Bear Creek Arsenal upper (formerly More's Machine Company)
My overall impressions on the build quality of the complete upper are positive, everything was assembled properly, the gas key is properly staked and they used Loctite on screws that you would assume need it, they also used it a few places that you wouldn't normally expect it..... More on that in a bit.
When I tore the upper down to prep it for cerakote I found that everything was tight and well torqued, the barrel nut was impossible for me to remove and I ended up having to take it to a friend that has a massive vice and reaction rod to attempt to get the barrel nut off, we ended up having to heat the barrel nut with a torch and used a 5 ft long breaker bar to get the damn thing to budge, once heat was applied we found that there was some sort of fluid melting from under the barrel nut and I can only assume it was Loctite or some other sort of thread locker, I normally tear down every assembled upper I get (or a friend has me look at) and add anti seize/assembly grease to the barrel nut so removing the barrel nut in the future for whatever reason is easier, I've made the mistake of putting 2k-3k rounds through a factory AR and then attempted to get the thing apart and it took WAY too much effort so from that point forward I've always added anti-seize/assembly grease and torqued it back to spec with good results.
The upper itself is definitely way down on the lower end of metals used to build ARs, it was extremely light and it felt cheap, the handguard is "okay" but again cheap, the way it attaches to the barrel nut is just about as bad as you would ever want to mess with because you have to make sure you index the screw holes to a certain position when you torque it down or your rail wont line up with the upper, the only solution is to torque the ever loving piss out of the barrel nut to get the screws indexed (see above) or use shims, when I reassembled the upper I used shims and it was easy enough to get everything lined up.
The Barrel is a run of the mill non chrome lined extra heavy AR barrel with a massive gas port, it is huge but it works. The upper came with a standard style bird cage flash hider so there is nothing good or bad about that, the gas block is a massive hunk of steel with 9 hex screws that hold it in place, 8 of them are fairly small and did not have dimples cut into the barrel for those, the 9th one is roughly a 1/4" pattern and the barrel was dimpled for that one so installation was straight forward.
I was shooting hand loaded 350 grain FTX projectiles with Starline brass, no clue on the powder or primers since I just paid a buddy for the reloading components and cranked out the rounds on his Dillon 650, I loaded 40 cartridges away we went.
Once at the range I gave everything a once over, added a bit more lube for good measure and shoved a loaded mag into the rifle and dropped the bolt, well the bolt wouldn't go into battery and the forward assist didn't help so I figured the OAL was out of spec on that round so I ejected it and soon found out the next 2 rounds did the same thing..... After going through various checks and everything else short of beating it with a hammer I dropped a round into the chamber and dropped the bolt onto the round and that seemed to work out the battery issue, the round fired fine and ejected normally but the rest of the magazine required me to put the rounds in one at a time and dropping the bolt onto the round, I switched to a P-Mag and it did the same thing so I put another 5 rounds through the gun one at a time, I loaded another surplus AR mag and 3 of the 5 functioned normally and 2 did not, well to make along story short after a 25 round break in period the rifle started working pretty much normally, I shot another 10 rounds from my stash and on one magazine I had one failure to go into battery but a couple of whacks on the forward assist did the trick and the last 5 went through with no issues.
I was offered more ammo but I can honestly say that 35 rounds of .458 Socom was more than enough in one range session and I still had 5 rounds of my own left, I was getting rounds on a 6" target at 50 yards with iron sights and the gun was in my opinion about 90% working properly so I called it a day, my plan is to add an optic and mount and continue the break in process, once my shoulder heals and I gather my own reloading supplies I'll continue the abuse of my shoulder and get this thing sorted out the rest of the way, all in all I am extremely please with the results, for the amount of money I have spent I think I've done very, very well.
So my opinion of the BCA upper is this, yes it is a cheaply made upper, yes they cut about every corner they could think of during the manufacturing process and yes I took a huge gamble and was flirting with "buy once, cry once" but in the end if someone is looking to build a 450 Bushmaster, .458 Socom or 12.7x42 AR on the cheap, I honestly believe that a BCA upper is worth the money, I have $299 in a .458 Socom upper so by saving $600 and not buying a quality high end upper I was fully expecting gremlins of one sort or another and I honestly am pleasantly surprised that everything has panned out as well as it has, if you're willing to "tinker" and have the knowledge to work out issues with the platform then the BCA uppers are well worth the money, as of now I think I have roughly $550-$575 in this build (not including the camo job) and in another session or two I expect to have a fully functioning big bore AR, that's not too shabby imo!
As an aside, the Kaw Valley Precision Linear Comp does a super job of keeping the concussion and muzzle blast from the .458 Socom down range, my friend has a 4 chamber muzzle brake on his .458 Socom and he cleared people out of the shooting benches 2 deep on his left and right, the people around me said the VG6 EPSILON on my 5.56 AR was WAY worse than the .458 was.
FYI, I am enjoying an adult beverage or 12 as I type this, so please excuse any misspellings or grammatical errors (yes I googled "grammatical errors") lmao!!