Saturday, September 3, 2016

Bootleg Inc Upper Receiver and Adjustable BCG Initial Impressions

Six months.  That's how long I'll probably have to wait before the ATF sends my tax stamp for a Griffin Recce 5.56 suppressor.  I already have a Surefire Socom 7.62, but I wanted a dedicated 5.56 suppressor that was a bit shorter and lighter for training classes and HD.  To help me manage the interminable wait, I decided to get an upper receiver started for my silencer in waiting.  The core of the action is of course the upper receiver and the bolt carrier group.  I decided to go with Bootleg Inc for this build.  They are a division of Primary Weapon Systems that makes their parts for DI rifles.  Despite the outward appearance, their upper is forged, not milled, and deletes the forward assist.  I've never had to use my forward assist, and it tends to get in the way of my ambi-charging handles.  Also, my choice of bolt carrier does not have the teeth for the forward assist anyway.  Aside from the light weight and nifty design elements, there are a few small enhancements I appreciate.  The dust cover pin is captured at the rear, so you don't have to fumble with a c-clip. The barrel extension mounting area is max spec and a tighter fit than my Aero Precision upper, necessitating a few taps of the barrel with a dead blow hammer to get it seated.  The finish is impeccable inside and out, with no tooling marks anywhere to be found.
Bootleg Upper - Right

Bootleg Upper - Left

Bootleg Upper - Top Rear

Bootleg Upper - Top Front

Bootleg Upper - Inside Front

Bootleg Upper - Inside Rear
I already have an SBR'd lower, so I've settled on an 11.5" barrel from Faxon Firearms with a mid-length gas system.  The short dwell time is offset by the additional back pressure from the can.  The overall length and weight are within an inch and a few ounces of a 16" barrel, but without the pesky noise and fireball.  Perfect for training, the indoor range, HD, and the impromptu 3-gun outlaw match.  While I don't plan on running this rifle without the suppressor, I still want the ability to "go loud" without having to locate an allen key to adjust a gas block.  I already have an 11.5" upper for a Surefire suppressor with an SLR adjustable gas block.  It works well, but adjusting it requires taking off the can to access the adjustment nut.  The Bootleg carrier only needs a cartridge rim and can be done without removing the carrier, unlike the one from Gemtek.  It has four vent settings, though I've only had to use the min and max vent positions.  The gas key looks properly staked and everything is finished in Isonite, a form of nitriding.  It doesn't have a glossy finish like other nitrided carriers such as my JP Low Mass.  I suppose the matte finish is more "tactical" but I prefer the easy cleanup of a slicker finish.  It's covered by the dust cover anyway.
Bootleg Adjustable Bolt Carrier - Right

Bootleg Adjustable Bolt Carrier - Left

Bootleg Adjustable Bolt Carrier - Top

Bootleg Adjustable Bolt Carrier - Adjustment
You have to provide your own bolt, firing pin, retainer pin, and cam pin.  Faxon Firearms offers matched and head spaced bolts with their barrels, so I went with theirs.  The other small parts are from Bravo Company.
Faxon Bolt
Since my upper isn't quite finished, I threw the Bootleg carrier in my current 11.5" upper using its Fail Zero bolt.  It uses the same Faxon 11.5" mid-length barrel, but with an SLR Sentry6 adjustable gas block.  I turned the gas black to its max setting to get an idea of how well the carrier mitigates excess gas.  I use an H3 buffer and standard weight recoil spring.  I didn't lube the carrier and the bolt was bone dry.  I fired 30 rounds of Federal XM193 unsuppressed with no problems, casings exiting at two o'clock.  I attached my Surefire 762 suppressor and fired five rounds to see how the over gassed rifle felt, then turned the gas adjustment to the full suppressed setting, and fired five more.  The difference wasn't earth shaking, but very noticeable.  The action felt smoother, the gun stayed flatter, and I didn't get any gas directly in my face.  However, being at an indoor range, an acrid cloud lingered to my right.  I didn't shoot weak-side, but I can't imagine it would be pleasant.  It only started burning my eyes after I dumped the remaining 20 rounds in the magazine.  For fun, I tried the other two settings and I could feel the increase in gas pressure with each one.  I do like the ability to add a little more gas if needed.  I then moved the dial back to the suppressed setting, and began to turn down the gas at the gas block.  I was able to go from it's max setting (15 from closed) to 9 from closed, before the bolt wouldn't lock back.  This tells me that it's still a little over-gassed for a suppressed SBR.  For a longer barrel it's probably perfect.  I ended up shooting only 120 rounds suppressed.  I had to take frequent breaks to let the can cool down, and I had two other guns to sight in.  At home, I examined the carrier for abnormal wear and fouling.  While I only shot four mags suppressed, the carrier and upper weren't as dirty as I expected, about as bad as shooting Wolf in a 16" unsuppressed rifle.  It may have been the lack of lube to attract dirt.  In any case, almost all of the fouling wiped off with an old t-shirt.
Bootleg on bottom is dirty, JP on top  is clean

Bootleg dirty - JP clean

BCG and parts after 120 rounds suppressed
One range session and 150 rounds aren't enough to make any definitive conclusions about Bootleg Inc's adjustable bolt carrier.  I also can't say for certain if I prefer it or the SLR Sentry adjustable gas block.  With the Sentry, I can get the gun perfectly gassed, without the eye watering cloud in front of my right shoulder.  With the Bootleg, adjustments are easier, though coarser, but it's less likely to fail or come out of adjustment since it's dealing with much lower temperatures and pressures.  My gut says to run the SLR on anything that isn't a defensive gun.  Since my new upper and Griffin suppressor will take on a primarily defensive role, that's probably where the Bootleg will go.

-Carry On

Thursday, September 1, 2016

SLR Rifleworks Sentry6 Adjustable, GB6 Micro Gas Block, and Barrel Dimpling Jig

My quest was simple.  To build a suppressed AR15 that weighs under 8 lbs unloaded.  Since I was using a JP Low Mass Bolt Carrier, I knew I'd need some way to keep the gun from overgassing the hell out of the bolt carrier with the Surefire 762Mini attached.  I looked at various adjustable gas blocks, but I didn't like their use of tiny coil springs and detents in one of the hottest areas of the gun.  Heat and springs don't mix.  I wouldn't be adjusting it often as the suppressor would almost never leave the rifle, but I wanted something I wouldn't have too constantly worry about.  

SLR Sentry6
Enter the SLR Sentry6.  Unlike other gas blocks, this utilizes a flat leaf spring tempered to 1400 degrees F.  Being external, it is exposed to cool air and is easy to rebuild if needed.  Everything is finished in Melonite QPQ to avoid corrosion, and the adjustment screw is in the front of the block, making adjustment a snap under any free-float rail with a long enough hex driver.  The black finish is smooth and even, and there is a starter hole on the right side for drilling and pinning.  There are also three vertical lightening cuts in the side, though probably more for aesthetics than weight savings.  SLR's Dimpling Jig made dimpling my nitrided barrel a snap with a hand drill.  I recommend a cobalt drill bit to make short work of the hard finish.  The Sentry6 slid easily onto the barrel with a little wiggling and fit snugly with zero perceptible wobble.  I added a dab of Rocksett to the set screw threads with a toothpick and secured them at 25 in/lbs.  Next I setup the barrel and gas block under a drill press and drilled the .125" retaining pin hole.  This is considered by many to be unnecessary.  While taper pins are the strongest way to secure a gas block to a barrel, they are used with a traditional FSB, where the front sight tower will likely get knocked around.  For a gas block protected under a rail, set screws and Rocksett should be secure enough.  However, I like my stuff to be bullet-proof.  I opted for stainless steel solid groove pins.  These are much stronger than a roll/spring pin so heat shouldn't be an issue at all.  The pin is actually slightly tapered, but unlike a traditional taper pin, three grooves are cut into the sides allowing it to compress inside a straight hole, so you can use a standard drill bit instead of a taper reamer.

SLR Sentry6 - Gas Screw
SLR Sentry6 - Grooved Pin
SLR Sentry6 - Bottom
SLR Sentry6 - Leaf Spring
SLR Sentry6, MI 10.5" G3 Rail, Faxon 11.5 Mid-Length, Surefire SFMB556
This setup gives easy access to the adjustment screw
SS Grooved Pins - McMaster-Carr Part# 98400A602
1/8" Cobalt Drill Bit - McMaster-Carr Part# 3069A16
The Sentry6 has 15 gas positions and makes 1 full revolution every 3 clicks.  My setup is an 11.5" Mid-Length Barrel, JP Low Mass Carrier, 3oz CAR Buffer, and Surefire SOCOM 556 Muzzle Brake with Warden attached.  I started at position 4 from closed.  I had to open it up to position 7 until it would lock back on a magazine.  With the Surefire 762 Mini attached, I had to turn the screw down to setting 4.  I then added an extra click open for reliability in case the screw got fouled.  More likely though, is that the metering screw will get eroded by hot gas and I'll actually need to close it some as it starts to over gas the BCG.

That was a few months ago.  Since then, I replaced the 3oz CAR buffer with an H3.  Shooting suppressed gets the action really dirty, and the extra weight of the H3 buffer helps with reliability after a few hundred rounds if I don't have a chance to cleam/lube the bolt carrier.  I had to turn the gas screw out to 9 from closed.  I'm also waiting on a Form 4 for a Griffin Recce5 Mod 3.  It, and the taper mount muzzle brake, are both a few ounces lighter than the Surefire and its brake.  I like using brakes with my cans to act as a sacrificial baffle.  I started building a new upper for it, this time ordering an adjustable bolt carrier from Bootleg Inc.  I liked the idea of adjusting the gas at the bolt carrier for three reasons.  First, the gas at the BCG is much cooler and at a lower pressure than at the gas block.  As the hot gasses erode at the adjustable gas blocks metering screw, it can allow the rifle to get more over gassed as time goes on.  Eventually it must be replaced.  Second, the heat generated at the gas block is going to effect its small parts more than at the BCG, increasing the likelihood of parts failure.  Finally, the adjustment at the BCG is much easier to accomplish, so I can "go loud" with just the turn of a cartridge rim.  I decided to stick with SLR for the gas block, this time their non-adjustable one.

The SLR GB6 Micro is a simple affair.  Like the Sentry6, it is has a Melonite QPQ finish, lightening cuts, and a started pinning hole.  It installed just like the Sentry6 with no drama.  You can view the install here: Dimple and Pin an SLR Gas Block
SLR GB6 Micro
SLR GB6 - Right
SLR GB6 - Left
SLR GB6 - Front
SLR GB6 - Rear
SLR GB6 - Top
SLR GB6 - Bottom
The SLR Dimpling Jig is as nicely machined as their gas blocks.  This version for .625" front sight bases is nicely anodized bright orange.  The machined ridges are unnecessary but a nice touch.  There are flats on the side for securing in a vice.  It has two sides. One for .400" spacing and one for .450"  I used Cobalt Bits from McMaster-Carr to and a hand drill at high speed to drill the dimples.
SLR .625" Gas Block Jig, Gas Port Locating Screw, Dimple Bushing

Position Locating Screw Over Gas Port
Mine slid on easily.

Lightly tighten Locating Screw into Gas Port

Drilling Rear Dimple w/ 5/32" Cobalt Bit
McMaster-Carr Part# 3069A18

Drilling Front Dimple