Auto-X Fil's Suppressed SBR Build

[Auto-X Fil]

I purchased a 16” Bushy almost 10 years ago now, and have run it pretty hard without any issues. It had all the typical “problems” of a commercial Bushmaster of this era – gas key “staking” that’s a joke, no stake at all on the castle nut, a non-F-stamped FSB. A taller sight post band-aided the FSB issue, I staked the castle nut, and I check the gas key when I clean it – no issues. But, I decided to get something nicer.

Part of the motivation is to get a gun that I have zero hesitation about. I could easily tweak a couple more things on the Bushy (primarily a better optic) and be there. The other part is that a new gun will have me all excited to shoot. I’ve been focusing on other things and only shooting a couple times a month lately. I haven’t even been doing my dry-fire drills like I used to. A shiny toy will remedy that, for sure.

Photos first, and then lots and lots of words if anyone cares.

Complete minus the Omega and T1:



77gr TMK handloads:



100yd test group (with a scope). First shot was high and left, and a bad trigger break was low and left. I don't usually pull shots like that, so I'm interested to see if this load continues to have flyers. The tight 8-shot main group certainly indicates MOA potential.



Verifying my irons at 200 on an SR-C target. The group is 5", 10-ring is 7". For BUIS on an 11.5" gun, that's certainly adequate. There was a bit of breeze from 10 o'clock, so I won't bump the sights one click just yet.



I found the following with my 50gr practice loads and the SLR gas block, with NO suppressor:

4 clicks out - unreliable feed
5 - occasional double feed
6 - reliable function, but didn't always lock back the bolt
7 - reliable bolt holdback. I settled here for now and will re-test with PMC Bronze when I find some.

I have about 300 rounds of 5.56 through it, plus 400rd of 22LR through a Spike's conversion kit. Aside from basic accuracy testing, I've been working out the ergos with shooting from cover, prone, weak-side, etc. I haven't used a Vickers sling before, and REALLY like it. I'm a red dot guy, and only use irons for high-power shooting. Adapting back to quick sight pictures has come quickly, although it's much harder weak-side. Overall I really like the ergonomics of the gun, and don't think I have much to change. The T1 will be absolute co-witness, since the sights will be down out of the way, and I like the current weld.

I like to keep sharp on engagement out to substantial distances, but prefer scoped weapons with .30cal projectiles past 300 yards. 200-300 is a wonderful max range for a carbine as far as I’m concerned. (Not the least of the factors in that decision is that a peacetime criminal threat 200 yards away provides a wonderful opportunity to run like hell and contact someone with a badge.)

I prefer, in general, to own one really nice tool, vs. a bunch of less-expensive and more specialized versions. This gun is biased towards home defense use, but as my only carbine, I want it to be as versatile as possible. To maximize versatility, a carbine needs to be reliable, tough, accurate, light, and compact. Since I have only just assembled it, only the last two items could be confirmed. I have just loaded up 1,000 rounds of M193 and M262 clone ammo to determine compliance to the first three requirements.

As I selected parts to meet these criteria, Bravo Company kept popping up at the top of the list. Their high quality and focus on simple, light, and streamlined design meshed perfectly with my goals. Prices are better than some of the other companies making more blingy top-flight stuff, which didn’t hurt. I sourced most of the gun from them, including:

• Upper receiver – I decided against trying to save too much weight with a slick-sided receiver. A robust mil-spec forged unit isn’t much heavier, and the dust cover and forward assist are in-line with my reliability goals. BCM offers an extra-snug barrel fit, and since I went with a BCM barrel, I knew the combo would work perfectly together. The fit was indeed perfect. Using a heat gun to gently warm the receiver meant it accepted the barrel with no effort, and a nice solid bottoming. Once cooled it could be moved by hand, but not easily.
• Gunfighter charging handle, Mod 4 – It operates very nicely, and the tight fit may or may not be part of the reason I’m not getting any gas to the face. The extended latch does bite into me when carrying the weapon slung across my front.
• 11.5 enhanced lightweight barrel – This is the heart of the build. 11.5” gives quite a significant velocity and range boost over 10.5” with most loads, and that extra inch of barrel in front of the carbine-length gas-tube helps provide a longer gas pulse to ease tuning. 12.5” was a consideration, but the marginal benefits were quite a bit less, and when I saw the weight specs of the BCM 11.5” ELW, it was a lock. You MUST run a free-float handguard with this barrel since the flange to mount the delta ring on is machined off, and it limits gas blocks to 0.625”. As both of those were OK with me, it was a great way to shave useless weight. The price is very good, as well. I skipped the fluting as the additional weight savings are tiny (half an ounce) relative to the cost.
• Intermediate A5 Mounting Kit – This is BCM’s own buffer tube that is designed to house the VLTOR A5 buffer system. I don’t think I need to go into detail – I fired it back-to-back with a standard system and it’s very noticeable. The BCM kit ships with an H0, but I have an H4 buffer on the way so I can swap weights and try H0-4 as I tune the gun.
• KeyMod Handguard – Although pricey, this unit checks all the boxes on paper – light, strong, and with a very robust attachment. Midwest Industries, Daniel Defense, Knight Armament, and others have good products as well, but none seemed to cover all those aspects as well as this one. Installation was a dream, and reinforced my idea of this as being the best-engineered handguard available. Now that I’ve attached some Keymod stuff, I feel silly for having reservations about the aesthetics. It’s awesome.
• KeyMod KAG – It’s cheap ($18) and light (1oz), so I gave it a shot. I’m actually considering moving it to the 7:30 position, although it would be wonky shooting weak-side that way.
• Keymod Grip panels – These are super light and low-profile. Most I’ve seen add a lot of diameter, but these don’t add any. I ordered another set so I can play with positioning more.
• Keymod sling mount – This allows me to experiment with sling positions. I can mount the rear to either the carbine tube end plate, or to the holes in the rear of the buttstock. The front can be moved around anywhere on the handguard. At the moment it’s all the way forward and I like it there. I should note this mount locks the swivel into position, instead of letting it rotate. I prefer that, some may not.
• Gunfighter stock – Their stock is a light, strong piece that has a very massive grip for adjustment, and absolutely nothing to snag. I really like this smooth, rounded approach for a stock. The built-in QD mounts work well.
• Gunfighter Grip (Mod 0) and Trigger Guard – This is a low-profile grip with a nice ergo fit to my hand, and a more vertical angle which is designed for shorter stock length and carbines carried close to the body. It blends seamlessly with the trigger guard, which offers just a little more room. Weight is a little heavier than the mil-spec grip, but that’s a small price for the improved ergos and a trap-door storage system.

To finish the upper, I grabbed these parts from other vendors:

• Gas tube – Colt. It’s a quality gas tube; not much to say,
• Bolt Carrier Assy, Chrome – Daniels Defense. I’ve used this in another build for someone else, and it’s a properly-built, precision bolt carrier assembly. The chrome may or may not cycle more smoothly when it gets dry, but it’s worth it for me just for the easy cleaning (especially since I got it on sale). The LMT enhanced carrier was considered, but I think it’s a band-aid for poor gas system and buffer weight tuning. I was a little bummed when I inspected the DD carrier:
• [IMG][/IMG]
• Kinda surprised to see that from them, but it was easy enough to clean up, and not in a critical spot. It proves the point that you should inspect everything, every time.
• SLR Sentry 6 Clamp-On Adjustable Gas Block – I debated this vs. the Syrac block for a long time. Those are the only two blocks which are very light and low-profile, and offer a positive lock on the adjustment screw. The SLR unit was not real cheap, but it oozes quality. There is no way this will ever fail on me or lose adjustment, especially hiding under that KMR. I should note the BCM barrel was not so over-gassed as others, and runs pretty well suppressed with gas wide-open and H0 buffer. That is with a 7.62 can, which might change things slightly vs. a 5.56 suppressor.
• Lower – We already had one in the gun trust as an SBR, so I just used that. It’s an Anderson and assembled just fine. The fit is pretty snug on the upper, and the magwell is disappointingly tight on my old first-gen PMAGs that I normally use at the range. They won’t drop free (I am aware this is a Magpul issue, not a lower issue). Mil-spec mags like my stash of C-Products and BCM 30-rds work great.
• Lower Parts Kit – Double Star has worked well for me in the past, and I find their trigger to be among the best LPK-based units available. I don’t need anything other than a clean break at reasonable weight, so I could save some money in that area. I inspected and function tested carefully, and it seems GTG. Trigger pull is once again nice and smooth.
• MBUS Pro from MagPul. There are lighter options, but this is super low-profile and clean. I considered skipping it entirely, but I like a BUIS as an option. I’m also grabbing these first to delay the next purchase a bit, since my wallet is hurting from all the BCM and Brownell’s charges:
• Micro H1 – Trijicon and Vortex and others have decent red dot sights, but AimPoint seems to be the only company that has rock-solid reliability and great ergonomics across the board. For a little more money than the other brands I get a bombproof, perfect little lightweight optic that I can trust completely. It’s also among the smallest and lightest.
• Co-witness mount – Daniels Defense offers a simple, light, strong, inexpensive mount. I don’t need a quick-detach, or else LaRue would be tempting. For less money and weight, the DD mount fits my build perfectly. I will do absolute co-witness since the BUIS is a flip-up style front and rear.
• Silencer Co. Omega – I don’t have this in my hands yet, either. Tests with .308 from some 3rd parties are not great in terms of noise reduction, although 5.56 looks similar to what was claimed (130-135db). The weight and length are excellent, and since I’ll be shooting supersonic full-power 5.56 anyway, it’s not like this was going to be a silent gun. I’ll take whatever dB reduction I can get in this tiny, lightweight package. It’s only 6.25” and 13oz with flat cap and direct mount. Also, at some point I’ll be threading my .308 bolt gun to accept it, and this can is rated for not just .308 Win, but 300WM as well.
• At the moment I’m running a YHM Phantom ULT. It’s pretty light, although longer, heavier, and (hopefully) louder than the Omega. By direct-threading an Omega with 5.56 end cap I should be 2” shorter and 2oz lighter.
• Sling - Vickers padded sling with MI HD flush QD swivels. I sewed the QDs on in order to save weight and streamline things.

Weight without sling, can (or brake), or optic came in at 5.3lb. It should be 6.5 or so with those items. That is ready-to-shoot with the MBUS Pro, and actually a bit lighter than expected, given that I chose durability over weight in my parts selections. A fluted barrel, some V7 and A2 trick lightweight bits, and a Ti gas block would have gotten it down to almost 5 flat, without any reduction in performance or durability, but the marginal weight gains were not worth the significant extra cost to me.