A Retrospective: The Colt 633 “DOE”

My Colt 633 DOE pistol build

Intro

It’s likely the same stupidity that led me to purchase a V8 sedan the same year a Democratic president took office that convinced me now was the time to build a PCC in the middle of a massive ammo shortage when 115 gr 9×19 is going for over 50% as much as it was 2 years ago. But damn it I did it anyway.

It is quickly getting to the point in the industry today that people are starting to catch on that as practical defensive tools, PCCs are kind of bad. Certainly not obsolete as they will still fire a bullet and kill somebody, but while the market has put a lot of effort into maximizing the potential of short barreled 5.56 ARs, it has largely been stagnant when it comes to pistol caliber carbine platforms.

That said, the big draw of PCCs is that they are fun as hell on the range and are (or rather, were) cheap to shoot. Also since the age of the submachine gun was planted pretty firmly between the 1960s and 1990s, you have a lot of neat Cold War designs like the Uzi, Skorpion, MP5, PPS, Vityaz, etc that you can collect for nostalgic or historical purposes. Or you can buy a soulless Glock mag compatible AR9, whatever.

I decided to take the former route and go with a neat Cold War aesthetic range toy. My original plan was to build a 10.5 inch barrel Colt 635 after my plans to make a CAR15 clone narrowly lost out to a DMR type build. While scouring online for a used 635 type upper, I ran across the 633 type upper you see here for not too much more from a private seller.

History

The 633 has a rather obscure history being adopted in limited numbers officially by the DOE and in VERY limited unofficial numbers by the DEA. It had a 7 inch barrel compared to the 10.5 inch used on the 635, handguards borrowed from the Colt Port Firing Weapon, unique to it front sight post and hand stop, A1 style carry handle upper receiver modified with a gas deflector (since it’s a straight blowback, that shield was intended to limit gas coming back to the shooters face, not deflect spent casings), A2 style lower receiver with a 9mm conversion insert pinned into the magwell, and a CAR15 style stock with 2 position buffer tube and a heavyweight buffer with spacer.

Magazines were based on Uzi mags with an extra notch cut in them to work with the AR15 mag release button. Action was the same boring direct blowback as the 635, though the 633 was known to come with a hydraulic buffer in some instances rather than the Colt standard heavy 9mm buffer. The 633 competed with the H&K MP5k for a DOE contract in the 80s with the Colt winning out.

Prototype 633 with ambi bolt catch/release, safety, and different style handguard.

The Build

Upper

Building one of these is not overly cheap or easy. There were only 5000 or so 633 models made and while a small number of surplus uppers made their way onto the civilian market a few years back, they have essentially dried up now and are expensive when you find them. The uppers are the real tricky part as that is where most of the unique parts come from.

To my knowledge there is only 1 company currently producing reproduction 633 uppers and that is Liemohn MFG (https://www.facebook.com/liemohnmanufacturingllc/) who manufacture at the very least their barrels and front sight bases in house, possibly more and mating them to Nodak Spud A1 uppers. They do have a waitlist though that you have to sign up for and put a deposit down on.

There was another company called Garrison Manufacturing that came up in some of my research that also seems to have sold 633 complete uppers and parts at one time, though I could not find an active website for them currently. Liemohn has only just recently started producing the complete uppers and my upper is not a genuine Colt as the receiver upper forge mark is an Anchor Harvey without a Colt “C” mark in sight so I believe mine was an older Garrison made upper based on pictures I’ve looked at online.

Lower

After you get the upper figured out, it’s usually pretty easy from there. Many standard AR-15 parts are compatible with 9mm lowers- lower parts kit, fire control group, buffer tube, castle nut and end plate, even the whole lower receiver given you use a pin in or screw in Colt mag adapter.

The other option would be to buy a dedicated 9mm lower receiver which at the moment is disappointingly difficult to come by. CMMG has moved to only offering lowers that work with their radial delayed uppers. PSA, Rock River Arms, Yankee Hill Machine, and Black Creek Precision all normally make a forged dedicated 9mm lower but are heavily backordered at the moment. Quarter Circle 10 and Spikes Tactical also make lowers but they are billet and will not follow the same lines as a 633 lower. Once your lower is sorted out, finish the build with a CAR15 sto- I mean a perfectly legal arm brace and you are good to go.

Magazines

Magazines are easy to find and made by several manufacturers including Metalform (the company that made the original Colt OEM mags), ASC, and C Products. Promag also makes a polymer Colt style 9mm mag but if you are seriously considering Promags in the year 2021, what the hell, stop it. I tested my 633 with a 32 round Metalform.

Initial Observations

First time out on the range I was expecting some hiccups as it broke in with a new buffer spring and magazine. In the first 100-120 rounds, I did experience probably 5 malfunctions and think that was mostly due to a combination of the break in period, loading the magazine fully, and the rapid firing I was doing. By the end of this period I was dumping strings of 7-10 (all on a steel ipsc at 10 yards which made me happy) with no malfunctions.

A few other interesting observations, while these historically came with 2 position buffer tubes (fully collapsed or fully extended), I opted for the standard modern 4 position just because they’re more common and in case I needed to put the stock somewhere in the middle like I usually do with AR carbines. However, in this instance, having it all the way extended really is a necessity. Maybe those of you with more trigger time on short barreled guns already knew this, but it was surprising to me.

Also, I had only ever experienced this with M16A2 or other fixed stocked AR variants, but there was an audible “sproing-ing” of the action during cycling that you could hear in the buffer tube with your head in the stock. A result of the heavier buffer and stock spacer at the back maybe?

Comparison

After getting this gun semi broken in, I wanted to compare my first 9mm PCC against some competitors. It’s been said that the blowback action of the AR9 combined with the heavy BCG makes the 9mm AR recoil heavier than a short barreled DI 5.56. I did not find this to be the case as I was able to borrow a friend’s 10.5” AR and comparing back to back 3 round bursts, the only appreciable difference I noticed was the way the gun moved directionally as a result of the recoil.

I took both guns and pulled the trigger 3 times as fast as I could and purposefully put no effort in keeping the gun on target to see what it would naturally do. The 5.56 stayed basically on the same elevation but ran off to the right slightly with each shot while the 9mm felt more like it was “wobbling” in my hands and danced around either side of the center ring of the target.

Just in felt recoil to the shoulder, I thought they were pretty similar, the biggest difference was the concussion and blast from my friends A2 birdcage-d 10.5 was MUCH harsher than the 9mm. With the 9mm the ever present “sproing”ing was more distracting than the muzzle report.

Next I wanted to compare my 633 to the darling of the 9mm PCC enthusiasts and it’s old rival in the DOE trials- the MP5. Sadly, it was not an HK or a K variant, it was a PTR 9c but it was the best I could source. It’s owner and I were eager to try out each other’s choice in 9mm bullet hoses and got to it. We both preferred the drum sights of the MP5 and the longer overall length aided in comfort and not feeling too scrunched up. The triggers were both unmodified and mostly comparable, but the familiarity of the AR trigger made me like it a bit more.

Ergos favor the AR more too, with comfortably familiar safety, mag release, and charging handle/bolt release. Last round bolt hold open was nice too. That said, while the ergos of the MP5 are lacking, the slap you get to perform on the charging handle will never not be cool.

Both of us were expecting from all we’ve heard about the legendary smoothness of the roller delayed action vs the crude and simple blowback that the overall shooting comparison would be a no brainer. Well… not really. I think both of us would agree that the MP5 was smoother and softer, but night and day different? Not to us. Call us inexperienced I guess, aside from these two guns the only 9mm carbines we’ve shot are the Kel Tec Sub2000 and the CZ Scorpion, but the feel of these we both agreed were pretty similar. I always thought reading about the DOE testing that the Colt won due to cost or the advantage of buying domestic, but now imagining shooting this next to an MP5k (even if it was in its superior PDW configuration) I could see the slight practical advantage of the 633.

Conclusion

I mentioned early on about buying a Cold War PCC vs a “soulless” Glock mag fed AR9. But practically speaking, aside from it using Colt mags and having a cool retro skin, this at the end of the day is just an AR9 that’s more difficult to mount optics and accessories to. For most people shopping for a practical defensive tool these days, the proposition looks silly. But if you already have your practical gun boxes checked, and are really into historical AR variants, I think this is a great gun to put into a 9mm PCC niche. You’re still getting the famed AR ergonomics, MOST of the part interchangeability, and arguably a more reliable if less sophisticated operating system.

And it looks super cool, which obviously trumps all.

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