Black Creek Precision’s Model GLK-F dedicated lower receiver is a winner. Extremely well made, they will run with small- frame glock pattern magazines and any standard AR or Billet upper. This solves the Colt pattern magazine problems of previous 9mm AR carbines and makes it practical and reliable.
What sets this lower apart is the high quality and their patented last round bolt hold open (LRBHO) feature. Built into the lower receiver and completely independent of the upper, the Black Creek pattented design works on two pivots and is very strong. It reinforces the bolt catch eliminating the issue of broken bolt catches from the bolt slamming.
Note to readers: If you are thinking this gun looks dirty, you are correct. Right after I built it, I ran 650 rounds through it. I am sure it would shoot 6,000 more rounds before it got so dirty that it slowed down. Collectors have clean guns.
Semi-auto 9mm Slim Cut lower receiver
Material: 7075-T6 forged aluminum
Finish: Hard-coat Anodized Mil-A-8625 Type 3 Class 2 – Matte Black
Weight: 0.7250 lbs.
Caliber Marking: 9mm
Safety Markings: Bullet Pictograms
Parts Included: Ejector, Lifter Arm, 6-32 Detent Set Screw, Upper Receiver Tensioning Screw, and Bolt Catch Dog Leg Set Screw
My initial impression of the lower was very good, the fit and finish are exceptional. The rear take down pin detent hole is threaded for a 6-32 set screw so that you don’t have to capture the spring with the end plate. There is threaded hole under the rear lug of the upper receiver for the tensioning screw. It comes with an excellent 9mm Feed Ramp, Ejector, Follower and a Bolt Catch Dog Leg Set Screw so you avoid that hard to install roll pin. These features make assembly easier and function more reliable.
The idea of a 9mm carbine is not a new one. Submachine guns have been around for decades, but carbines are a little larger with better ergonomics and are more manageable. In 1981, Marine and genius firearms designer Maxwell Atchisson was thinking about the XM-177.
The XM-177 was a variant of the M-16 with a 10.5″ barrel. The short barrel wasted a lot of energy as flash and noise, and got very dirty quickly.
Atchisson realized that the XM-177 would be much better if chambered in 9mm. He was a genius and could just do stuff like that. His 9mm gun was a closed-bolt, simple blowback-operated select-fire machine gun.
His blowback system consisted of a heavy bolt resting against the base of the 9mm cartridge case, with a heavy buffer and recoil spring compressed by the kinetic energy of the bolt when it moves back under recoil. The stored energy of the compressed spring then drives the bolt forward back into the firing position. This eliminates the whole gas system, allowing the use of very short barrels. For close quarters, it had all the energy it needed in a small, low-recoil package, with the great ergonomics of the M-16. A 10.5″ barrel is the sweet spot for 9mm, giving nearly optimum energy.
Colt took over the project and in 1985, introduced the 9mm SMG. More interested in parts commonality with the M-16 than innovation, they came up with a rough, mass-produced product still sold by Colt today. The Marine Corps adopted the 10.5″-barrel model for the Fleet Antiterrorism Security Teams (FAST), and it was used by DOE, DEA, U.S. Marshals Service, and the U.S. Diplomatic Security Service. The Bahamas, Bangladesh, Malaysia, and Panama also fielded the SMG.
There were several problems with the SMG. A special heavy black buffer was designed to keep the cyclic rate below 1,000 rpm, as a standard 5.56mm buffer would run at 1,250 rpm. Because the direct-blowback design created such high bolt speeds, bolt catches, as well as the trigger and hammer pins, were prone to breakage. The pins were upgraded to nickel-plated stainless steel.
Colt decided to use modified Israeli UZI magazines. Their version has narrow feed lips, making them very hard to load, prone to double feeds, and they wear quickly. Glock magazines solve this problem.
Inspired by the SMG, Black Creek Precision has reinvented the AR in pistol calibers and improved it substantially by adopting the solid and widely available Glock mags and adding last round bolt hold open.
I selected the CMMG Lower Parts Kit for this build. People often under estimate the importance of the parts. All parts are NOT created equal. Before the last assault weapons ban in California, I was helping buddies put together lowers. In the week before the ban, I assembled 32 lowers myself and saw a hundred or so others come together. Because parts were coming from everywhere, there were many brands used.
The CMMG kits were by far the easiest to install because the parts are made to exacting specifications and the colored parts bags organize your build and set your parts up in a logical order. Nothing is more frustrating than having a part that doesn’t fit.
Because a 9mm AR is so perfect for short barrels. I choose a pistol build with a Gear Head Works Tailhook Pistol Brace. These braces look great and really perform weither open or closed.
The simplicity of blowback guns has always interested me. Since most blow back designs are full auto, most shooters don’t encounter them.
The blowback operation of the 9mm AR-15 drives a very heavy bolt (normally 16 ounces) much harder than a standard AR-15 BCG. The energy of the 9mm bolt needs to be dampened to reduce wear, reduce recoil and minimize sight movement. Hydraulic shock absorption is very effective—it is science.
The Blitzkrieg hydraulic buffer shoots softer and runs quieter than any conventional AR buffer. Its weight and length have been optimized for the 9mm application so it runs reliably, softens recoil and stops the bolt just behind the bolt catch using any 9mm ammo type. It dampens bolt impact for a soft landing which completely eliminates spring vibration and noise.
The Blitzkrieg buffer and Orange Sprinco spring made this build run like a Swiss watch—timing everything perfectly while reducing felt recoil. I strongly recommend this buffer and spring combination.
I gathered my equipment for the test. I had an assortment of 9mm and .40 ammo. The 9mm was mostly Armscor 9mm Luger 115-grain full metal jacket. It is great ammo at a fair price.
I used an ETS C.A.M. loader to load up my mags. Some people ridicule the use of magazine loaders, but when you are loading 1000 rounds at a time, it makes a difference. I had plenty of ETS mags and Glock factory mags of various sizes as well some 33-rounders of uncertain Asian origin. They all worked well.
9mm AR uppers used:
- Tridentis Tactical with a 16-inch barrel with Trijicon Reflex Sight
- JP Rifle JPGMR-13™ 9mm with a 14.5-inch pinned barrel with Trijicon Reflex Sight
- Lone Wolf G9 Carbine in .40 caliber with a 16” upper with Aimpoint Comp-M
- Modular 9mm dedicated upper with a 16″ barrel decked out with Mission First Tactical foregrip and sights.
The GLK-F had a great fit with every upper I tried. It functioned perfectly with all the magazine, ammo and barrel combinations I tried. With both 9mm and .40 caliber, it performed like a champion. The bolt hold open worked well and the ergonomics of the mag release is even better than the original AR. It went together easily with the CMMG parts kit.I highly recommend the Black Creek Precision GLK-F for your next build. The precise dimensions make it an easy build and the lack of a gas system makes pistol caliber uppers easy. Perfect for a first build. Who doesn’t have glock magazines around?
Get your very own Black Creek Precision Model GLK-F Dedicated 9mm Lightened Forged Lower Receiver Assembly for Glock Mags HERE MSRP: $219.00
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