@WestDesertPRS Hopefully the below info will be useful to you and others. That said it's a long post and I don't want to hijack your thread. I may start a dedicated BCG resource thread and move this post there.
I am running 2 different brands of BCG.
Not saying others suck, it's just what I chose. I'm not listing every spec for these, just the highlights that mattered to me beyond mill spec. Things like HPT/MPI batch testing etc are a given for a quality BCG.
There are a lot of good choices available now.
1. Toolcraft - From ArmorAlly or B. Kings firearms
- Cost is very reasonable
- Great selection of bolt head sizes & coatings
- They use quality grade 8 gas key fasteners and stake them properly
- They are a large company that will be around for the foreseeable future
- The 2 I have used both head spaced without issue.
- The Master AR armorers class I took (School of the American Rifle), said Toolcraft do not have issues with head space or failure. He works hundreds of AR's a year.
- In the armorers class I gauged my large frame Toolcraft bcg & it was in spec using mil gauges for gas key id, gas key flare, bolt bore id, bolt ring seal id, bolt tail id, firing pin protrusion, & firing pin bore id
I have 2 of these
- 6.8 SPCII DLC coated. round count is only about 200, been flawless so far.
- DPMS large frame AR 308 nitrided, double ejector, & small firing pin. I picked Toolcraft for this because they had the small high pressure (6.5C) firing pin, whereas many of the large frame BCG's only use the large pin 308. Round count is about 120. The double ejectors threw brass 30' until I got the gas turned down. They did not have a small firing pin single ejector option when I purchased mine.
2. Sharps Rifle Company XPB BCG purchased directly from Sharps (currently on sale for $169.00 + 15% off)
- Cost wise, these have a lot of features for the $
- DLC coating, I think Sharps was the first to offer this on a BCG
- Beveled bolt lugs. I have no proof, but it seems logical to me that this profile would have no down side & likely to run better/longer under extreme conditions.
- Bolt, carrier, ejector, & extractor pin are S7 tool steel. These S-7 parts under go a 24 hour thermal cycle heat treat before DLC. FYI...S-7 tool steel is not only stronger, it's an ideal base metal for DLC.
- Gas key is attached with quality grade 8 fasteners and correctly staked.
- Bearing surface is increased. See pictures below. The bearing area adjacent to the gas key has been widened.
- Tail section is slightly enlarged to better center in the buffer tube (less rock)
- I have head spaced 2 of these 1 x 223 Wylde & 1 x 300 BO both were on the money
- Gas ring is mil spec and friction is also in spec with the DLC bore. The test for this is to stand the assembled BCG on the bolt face while it is extended and the weight of the carrier should not push it in.
- I gauged one of these thoroughly. One area is not mil spec. It is the bolt tail hole at the back of the carrier body, it's oversize from mil spec by .002-.003. FWIW - I saw a JP BCG fully guage inspected and it was loose in this same spot. Probably intentional by Sharps & JP considering how precise everything else was, but they do not provide rational. I suspected the only negative is a little more gas leakage out the back, therefor these BCG's are a little less gas efficient. This is not a bearing surface but if a close fit (mil spec), and it carbons up it could cause issues.
- I've since watched a video review (on Sharps home page) where they describe a little extra gas in their face on short barreled suppressed. The oversize bolt tail hole no doubt. The other interesting side affect was when they took an over gassed 5.56 (launching brass @1-2 o'clock) and then screwed a can on. I figured it would over ride the mag, but instead the brass ejection actually came back around to 2-3 o'clock. Maybe the oversize hole is acting as a pressure release when suppressed.
I have 2 of these running and a 3rd build in the works. I think they are one of the best values in BCG out there right now.
- Sharps XPB Low mass in a 223 Wylde 16" mid gas non adjustable gas block with VLTOR A5 buffer (Std. weight). I'm right at 1000 rounds in this so far and it has not malfunctioned once. It is a little over gassed, but shoots so well I haven't bothered to put an adjustable block on it. A couple times I've been at the range and someones AR wouldn't cycle well (shitty ammo suspected), so they handed me a mag with there crap steel Tull and some other crappy stuff to try. It's eaten everything tried so far. I recently used it for a 200 round unconventional shooting position combat carbine class. Most of the drills started laying down, on your back, side etc. It was fucking raining cats and dogs and I have an obnoxious 3 port Coda break that was blowing mud and grass everywhere (lesson learned). Gun was filthy, but ran flawless.
- Sharps XPB std. weight in a 300 BO, 9" barrel, pistol length gas, Maxim CQB brace with JP silent capture heavy buffer, and adjustable GB. I have the gas wide open and probably need to lighten the buffer weight to get in the adjustment range of the GB. It has almost no recoil. So far I only have about 150 rounds through it with Winchester white box 125 grain & reloads with 125 grain SST's.
A few notes on gas keys to be aware of.
- Many aftermarket BCG's use YFS bolts in the gas key. They are clearly marked YFS on the head. YFS stands for Fang Sheng Screw Co., Ltd (YFS). If you have these they should be pulled out and replaced with US grade 8 allen heads from a reputable source such as "OCKS screws" from forward controls. I have not had any personal experience other then the Armorers class where the instructor had a box full of wrecked BCG's with broken gas key bolts & all were YFS.
- Proper staking of the gas key fasteners requires a special tool that indents both sides with a blunt point. Even better is to squeeze directly in on the sides like Sharps does. When the gas key bolts are torqued to 58 in lbs they are under tension near their yield point. If staked improperly it bends the already highly tensioned head to one side then the other. I think this is why sometimes the bolt head will remain in place even though it's broken. Or back out with almost no effort because yield strength was exceeded during staking. Only way to catch it is to try reverse torquing 20 in lbs. It should not move and you should do this test to all new BCG's.
DLC = "Diamond Like Carbon" It's considerably harder and slicker then nitride. DLC only adds or builds up avg of 3 microns or .0001 to the surface. It also penetrates the surface of the base metal, so it's ideal for parts requiring close tolerance be held (Head Space).
This coating is just plain bad ass and I'm glad it's gained a strong foot hold in the fire arms industry. I first worked with DLC about 15 years ago in race engines on
S-7 tool steel (
Hint) wrist pins. This was in NASCAR/Winston cup heyday. Restrictor plate motors were running insane compression ratio's (15.5 - 17 to 1) to compensate for lack of carburation. We were pulling so much crank case vacuum on those engines that tiny oil jets had to be added to spray oil directly at the wrist pins, & still they'd barley complete a race. Hell if RPM's weren't kept up especially through pit row they would detonate & self destruct. Adding DLC coating to the wrist pins changed everything. At the same vacuum and compression levels, DLC allowed us to shrink wrist pin diameter and length to lighten them.
Pictures of Std weight Sharps XPB/DLC BCG
Here is a video by the instructor who's class I took. It illustrates most of the QA/QC checks that should be done to a BCG.
In the class we also checked firing pin run out, pin guage checked the gas key bore, used a fixture to check gas key alignment with the upper gas tube hole, and checked bolt lug clocking with the barrel extension.
