Larry Vickers recently posted a cool video on the Colt 9mm SMG.
Long ago I had a Colt AR6450 9mm upper. I bought it along with a used VM Hitech Uzi Magazine adapter. It was fun, but I remember my first impression was that the 9mm felt like it had more recoil than a 5.56.
I can’t find a picture of the upper I had, but it looked much like the one in the picture above. With Uzi mags and the VM HiTech Block it ran well. I eventually replaced the upper with a flat top and added a KAC M4 RAS to have a quad railed handguard. Later I decided I wanted something shorter so I sold the upper and bought a RRA 9mm upper. I can only find one messy photo of that setup:
That upper ran fine, but I remember I didn’t like that the bore wasn’t chromed. The barrel profile on the RRA upper was so heavy that the RAS barely fit, and I remember that 10.5 inch upper feeling heavier than the Colt 16 inch upper it replaced. I really didn’t like it. From them I vowed not to sell something until I had its replacement in hand already. A rule I still usually don’t follow.
This picture found online shows the VM HiTech block well. It allows for use of unmodifed Uzi mags, but you have to use the new mag release at the bottom left side of the block. I’ll admit I hit the standard release more than a few times while using this block and dropped the entire block.
While it all worked, I ended up getting rid of that whole setup.
Some time back I saw that Colt was making a new version of their 9mm SMG and 9mm AR15s. Pretty much the only change was that they were coming from the factory with a flat top upper. They offered 10.5 inch barreled model, the 6991, and a 16 inch model the Colt 6951. I saw a cheap used 6991 upper, so I picked it up along with a Hahn Precision mag block.
Here is a pretty lousy pic of the setup:
I’ve had no issues with it, and it is fun to shoot. But really, pistols calibers are not what the AR is best at.