Building an AR PCC

Over the past few months I wrote a series of posts about assembling an AR at home. I hope this helped some of our readers with their projects.

What I did not mention is that I’ve been sourcing parts to build a Colt Model 6450 9mm Carbine replica (the commercial version of the full auto Model 635), and it’s finally done.

Throughout this post are links to some of the 9mm AR PCC (pistol caliber carbine) specific parts. It’s an incomplete list, because I already had some of the parts and certain parts have become difficult or impossible to source in the last couple of years. For example, the proper retro receiver halves are almost unobtanium right now. NoDak Spud was the premier source of retro AR upper and lower receivers, as well as some other specialized parts, and they are no longer in operation.

According to Mike, the former owner of NoDak Spud and current head of the Harrington & Richardson brand, “It will easily take until summer before we have things rolling. So many elements need to come together.”

But enough of that! On to the build details.

The author's Colt 6450 Reproduction

Two of the major considerations for proper operation of a 9mm AR PCC are buffer length and the combined weight of the bolt and buffer. The 6450 is a straight blowback firearm, and the bolt is not locked at the moment of firing; therefore, the weight of the bolt and buffer are of considerable importance. More details can be found on this website. Furthermore, a 9mm bolt is shorter than a 5.56 bolt carrier group. This means the 9mm buffer and bolt will go further back into the receiver extension in recoil. This can cause two issues:

1. The front of the fire control pocket is exposed at full recoil, increasing the chance of fouling, debris, or even an empty shell casing winding up in there and interfering with operation.
2. The bolt has more forward travel, picking up more speed before hitting the bolt hold open, potentially damaging or breaking that part.

There are two options to resolve the buffer length issue: either a buffer with a longer base or a spacer that goes at the rear of the recoil spring. Both will work well to ameliorate this concern, so it’s buyers choice.

For the buffer, I went with a KAK Industries configurable buffer kit. This comes with three sets of weights, allowing the user to configure them for best performance. Me being me, I accidentally ordered the standard length buffer instead of the extended version, so I had to get a spacer for the other end of the recoil spring.

Assembly of the firearm is pretty straight forward. There are only two elements of significant difference from a standard AR.

1. The magazine well adaptor. There are several different styles. Some are installed through the top of the lower receiver, others through the bottom. The one I bought inserts through the bottom of the magazine well and is held in place by two set screws at the mag well opening and a third screw at the top, making it very secure.
   
   Being of the Colt style, my mag well takes modified Uzi magazines. Either vintage or new production. Uzi magazines need to be modified by having a magazine catch hole cut in them and the spine of the magazine relieved at the top so the bolt has proper clearance. Uzi magazines altered in this manner will function in an AR style PCC, but they won’t lock the bolt back after the last shot is fired.
   
   
2. The ejection port door assembly. The original Colt style uses a shortened door and a rubber gas deflector. To clarify, it’s not a brass deflector, it’s a gas deflector. As I mentioned, it’s a straight blowback system, and the bolt starts moving at the moment of firing. Excess combustion residue exits the ejection port fairly early in the extraction process and without the gas deflector, could pepper the user in the face.
   
   Installation of the port door and gas deflector is only slightly different than a standard AR, but may require an extra hand due to the additional parts needing to be wrangled.

Once everything was all together and had passed the mechanical function and safety checks, it was time to test fire my creation, and I’m happy to say it operated flawlessly. Brass ejected consistently and landed in about a three foot circle. After dialing in the sights, accuracy was excellent and it cut one ragged hole in the target with a few flyers that were the fault of the shooter rather than the gun.

50 rounds at 10 yards freehand.
Not too shabby!

While I don’t expect this style of PCC is everyone’s cup of tea, I’m pleased with how it turned out and it’s a welcome addition to my collection. This was a fun project, and a welcome distraction from both personal and global troubles.