By Dave Bahde
The 300 Blackout (BLK)
While a very late-comer to the caliber, once introduced the 300 Blackout (BLK) has slowly but surely become a favorite, especially in shorter barrels. Even with a 9-inch barrel you still get usable terminal ballistics without all the reliability issues the 5.56mm presents. Add a suppressor and the difference is striking. Using full-power 110- to 125-gr. bullets and any number of suppressors they just flat out work. No muzzle blast, your hearing remains intact and they can be as reliable as this rifle system gets. Most 300 BLK rifles are direct gas impingement models keeping them simple, light and easy to maintain. For across the room, or the street, these are solid performers. But what if you wanted a bit more?
Testing dozens of short AR rifles in various calibers, the 13-inch barrel seems to be a sweet spot. It has been true for me in 7.62 NATO (.308 Win.), 6.8 SPC, 7.62 x 39mm and 5.56 NATO. Reliability tends to be better, muzzle blast is less, and when using the 7.62 x 39mm velocity loss is lessened. Logically, it seemed the 300 BLK would be about the same. Looking to my friends at Primary Weapons Systems, I borrowed one of their new MK112 300 BLK carbines. With its 12.75-inch barrel, not only could the theory about barrel length be tested, but it was a piston gun, not something you see in this caliber.
Primary Weapons MK112 300 BLK
The MK112 300 BLK ($1,949.95) is an SBR (short barreled rifle) and must be registered as such with the BATFE. The payment of $200 tax is required, but while the process can take a few months, it’s relatively straightforward and worth both the cost and the effort.
Primary Weapons Systems’ piston system is about as close as you can get to that of an AK gas piston in an AR. It has proven incredibly reliable in every caliber tested to date, is lighter than most tappet systems, runs cooler, and operates well with short barrels. The MK112 uses that same system with a shorter length piston (gas block) and a 12.75-inch barrel. Total gun weight is 6 lbs., 4 oz., and overall length is 29.5 inches.
Furniture consists of a Magpul MOE 6-position collapsible buttstock and MOE pistol grip. The free-floated handguard is a PWS design with full-length Picatinny top rail, KeyMod flats at the 3, 6 and 9 o’clock positions, and 5-slot Picatinny rails mounted all the forward on both sides. It comes with a set of Magpul MBUS flip-up sights and one 30-round PMAG. The MK112 300 BLK is built on forged and machined receivers, with the upper being a proprietary design to accommodate its AK-47 type bolt carrier and gas system. A QPQ-coated 12.75 inch barrel with a profile designed to lose weight, not accuracy, is standard equipment.
Chambered in 300 BLK, and rifled at a 1:8 twist rate, it’s button rifled using M4 cuts for proper feeding. Isonite coating is becoming the standard for any hard-use AR. Set up for use outside the range a Triad flash hider is installed. PWS bolt carriers and bolts are made from tool steel exceeding military specifications then nickel-Teflon coated for reliability and ease of maintenance. Designed specifically to work with PWS rifles, they are some of the most advanced on the market and as strong as can be made.
I mounted the MK112 300 BLK’s complete upper on my registered, selective-fire Primary Weapons Systems Mk1 lower receiver. It’s equipped with a Geissele Super Dynamic Combat trigger and BAD ASS 60 degree safety levers. The grip is a BCM and the stock is a VLTOR. Law Tactical’s Gen 3 folder makes for a truly compact rifle. PWS bolt carriers just need a different extension and Law Tactical has them. Installation is simple allowing this rifle to fit perfectly into my Arcteryx Khard 60 pack.
The primary test venue was a Heliborne Assault class put on by Aegis Academy (www.aegisacademy.com). Designed as a shooting “experience,” it consists of a couple days of range work in preparation for live fire out of an MK-6 “little bird” helicopter. Targets are from 25 to 100 yards, weaving in and around a canyon in the California Desert. Given this mission, the MK112 BLK was equipped with a Trijicon 1-6X VCOG (trijicon.com) using a segmented circle reticle calibrated for 300 BLK. EoTech’s MRDS was added at 1 o’clock on a Trijicon mount and zeroed at 50 yards. The Law Tactical Gen 3 folder allowed it to fit in the Khard 60 pack, even with a Gemtech GMT-300 suppressor attached. Designed specifically for the 300 BLK, the GMT is light and provides proper baffling (www.gem-tech.com). Ammunition was supplied by Gemtech and International Cartridge. Most testing was with the 147-grain FMJ from Gemtech, while ammo for shooting from the chopper were frangible using 149-gr. bullets. Magazines were all Gen 3 PMAGs, and illumination was provided by a Surefire Scout. I also installed a Zero Bravo hand stop to round things out.