We had been looking for a 9mm carbine for a while. We were drawn to the 9mm because we could shoot steel at short distances and it would be cheaper to shoot than 5.56.
We were drawn to Quarter Circle 10 for two reasons. Reason 1, It takes Glock magazines. Glock magazines are affordable, reliable, and readily available. A 9mm AR-15 Carbine that takes Glock magazines would be easy to integrate into our current system. Reason 2, unlike other 9mm Glock lowers the Quarter Circle 10 lower offered a last round bolt hold open feature.
The Glock Small Frame Lower from Quarter Circle 10 is impressive! The quality of machining, the finish, and the fit are top notch. The lower is machined from a 7075 T-6 aluminum.
There is nothing better than starting with a blank slate when doing an Ar-15 build. For the upper we selected an Aero Precision forged upper without the forward assist. The barrel is a Wilson, 16 inch 1/10 twist, purchased from JSE Surplus. The bolt is a JP Enterprises 9mm bolt that comes machined ready to use with the narrow glock magazines. Quarter Circle 10 is now offering their own bolts, at the time of purchase they were not. The handguard is a BCM kmr 13 inch free float rail. To finish the upper, we chose a BCM Gunfighter mod 4 charging handle.
A 17 round Glock 17 mag pictured.
For the lower we used a mil-spec lower parts kit with a ALG advanced combat trigger, a mil-spec buffer tube and spring, a Rock River Arms 9mm buffer, and a Magpul grip and a CTR stock. We fabricated a buffer tube spacer from an old buffer that we cut down. The spacer is to prevent the bolt from over traveling and possibly damaging the bolt catch.
Today we ran a flawless 250 rounds through our 9mm carbine. We shot a mixture of factory full metal jacketed ammunition and various full metal jacketed reloads. They all functioned the same, the only difference was the distance they ejected from the gun. The last round hold open feature worked as advertised. Recoil from the 9mm was noticeably less than its 5.56 counterpart. Knocking over steel plates has never been more fun!
We give the folks at Quarter Circle 10 a five star rating!!!! The fit and finish of their lower was outstanding. They were great to work with and shipped our lower the day after I ordered it. Check out their current offerings at www.qcircle10.com
Here is a video link http://youtu.be/yRr4xa3HGLs