This is Brownells’ 733 C7 11.5” Upper Receiver assembly, a copy of the 11.5-inch-barreled Colt 733 top end with a C7 receiver. This is a bit of a retro piece that I built up into a full retro gun, and if it doesn’t look familiar to you, it should. This (minus the full-auto capability) is the exact same gun Robert DeNiro and Val Kilmer were using during the greatest gunfight ever captured on film, the bank robbery scene from “Heat.”
But Colt’s 733 has far more history behind it than just one classic movie, and there are some interesting features here. Please note: I bought this upper with my own cash. It wasn’t sent to me for testing, so I have no motivation to do anything other than tell the brutal truth in this review.
Colt started making short-barreled versions of the M16/AR-15 way back in the 1960s, and a complete listing of them would fill this entire magazine. They were generally referred to as CAR-15s, that “C” standing for Carbine, and the term CAR-15 hung around until the introduction of the M4 in 1994. But they were generally short runs or experimental models — the “XM” in the XM-177 classic carbine of the Vietnam War stands for “eXperimental Model.”
Colt made 10.5-inch variants back in the day for use in Vietnam but found they had some reliability issues due to the short dwell time. The gas port was very close to the muzzle, and inconsistent ammo and dirty operating conditions sometimes produced less than optimal gas pressure, causing cycling issues. Stretching the barrel length to 11.5 inches seemed to solve almost all of those cycling issues. Officially and sometimes otherwise, these guns were called the Colt Commandos, and the Brownells upper end is a (mostly) faithful reproduction of later (post-Vietnam) versions of the Colt Commando.
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The secret to the popularity of the 733 is the barrel. An 11.5-inch length seems to provide the best of everything when it comes to SBRs. It is short enough to be handy, long enough to provide good velocity from most ammo, reliable, and — perhaps as important as anything else — that original pencil-barrel profile, which you see in this Brownells build, keeps it light.
Brownells’ 11.5-inch barrel has a lightweight A1 profile. It has a 5.56 NATO chamber, a 1:7-inch twist, and a chrome-lined bore and chamber. That 1:7-inch twist rate isn’t period accurate, as those original guns likely had a 1:12-inch twist rate, but it will allow you to shoot heavier bullets than Vietnam-era 55-grainers without worrying about them keyholing. It of course has a carbine-length gas system. It is tipped with a model-correct A1-style birdcage flash hider, which has slots on the bottom (unlike the solid-bottomed A2). The barrel has been given a phosphate finish.
Just behind the muzzle you’ll see a fixed A1 front sight tower — not “F” marked for those of you wanting clone-correct builds. The front sight tower is pinned in place and has a bayonet lug at the bottom front and a sling swivel at the bottom rear. Brownells’ 733 has the original-style narrow round CAR handguard, which are black plastic but have an aluminum heatshield inside. At the back is an original-style narrower delta retaining ring.
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The early CAR-15 handguards had only six holes, whereas later slim CAR round handguards, such as the one found on this upper, have seven holes. Does it make a functional difference? No. But a lot of companies are now making retro parts for your retro CAR builds if you’re that picky.
The upper receiver of the 733 is interesting. This is/was a transitional model, introduced after the Vietnam-era CARs but before the M16A2 came out, and the receiver you see here is the C7, originally produced by Colt Canada and later added to many U.S.-made Colt carbines. The C7 has the original carry handle, rear sight of the M16A1, and the teardrop-shaped forward assist, but it also has the “Burton bump” shell deflector found on all the M16A2 rifles. If you rewatch 1995’s “Heat,” you’ll see Neil McCauley and Chris Shiherlis are running 11.5-inch Colt Commandos with C7 upper receivers and 7-hole handguards on the streets of downtown Los Angeles as they try to break contact with the LAPD.
The A1 rear sight is simple. It has two apertures, one for close-range targets and one (marked “L”) for longer range. With my nose against the charging handle, this aperture is just large enough to accommodate the width of the front sight post wings. For a short-barreled carbine, it’s the perfect blend of speed and precision.
The rear sight is adjustable for windage via a wheel on the side of the fixed carry handle that is designed to be turned using the tip of a cartridge. The front sight is the standard post, adjustable for elevation using — again — the tip of a cartridge. Not quick to zero, but once you are dialed in, they won’t move.
If you’ve never run an AR with a carrying handle, note that there is a hole in the middle of the handle, and various types of optic mounts attach to the carrying handle using that hole.
This upper receiver assembly comes complete with a mil-spec bolt carrier group with a properly staked gas key. You get a standard GI-style charging handle with this upper.
This retro carry handle upper doesn’t have some of the tweaks and upgrades you’ll see in modern ARs, but honestly, what will shock you is just how light and handy it is, something lost in most modern ARs and even SBRs. The complete upper receiver assembly weighs 3 pounds, 8 ounces, according to my digital scale. What does that mean? It means if you use it to build up a carbine, and you use a GI-style lower receiver, an original polymer CAR stock, and an A1 or A2 pistol grip, the total empty weight of your 733 clone will be just 5 pounds, 6 ounces. That is light, and it feels just as light as it sounds.
I did just that. Wanting a replica of the carbine made famous by “Heat,” I decided to build up a lower receiver and Form 1 SBR it. I didn’t have any period correct lower receivers, but I found an old Rock River Arms lower receiver in my basement that was so old I truly didn’t remember buying it. I checked with RRA and had them run the serial number, and found my lower was “born” in December 2001 and sold as a stripped lower shortly thereafter — to me. So, it was not quite old enough but close enough for me.
If a modern lower receiver isn’t good enough for your build, several companies make retro lower receivers. But be aware that instead of costing $50 to $100, those retro lowers, some of which even having correct markings, will cost you bunches of cash. International MilSpec Company has a fascinating catalog of lowers. Their Commando XM177E1 lowers (properly USGI roll stamped, “PROPERTY US GOVT COMMANDO CAL. 5.56MM” with correct serial number range) would be perfect, but they’re $575 just for the stripped lower.
Into my Rock River lower receiver, I installed a CMMG GI-style trigger group that I pulled out of a gun years ago but set aside. For a GI-style fire control unit, it provided an excellent 5¼-pound trigger pull. That’s as good as you’re going to get with a GI-type trigger. Please note that I’m not saying “mil-spec trigger group,” as the military never has had a spec for a semiauto trigger group.
Onto a (modern, 6-position) mil-spec carbine buffer tube, I installed an original plastic CAR stock. These are small and shockingly light (4.2 ounces), and the back end is aggressively textured to keep it from slipping off your shoulder. It has slots for attaching a sling. I pulled this off a gun sometime in the ’90s and kept it around. B5 Systems is now making retro CAR-15 stocks to the original GI specs in both black and OD green.
For a period-correct build, I should have installed a flat GI triggerguard, but those leave a gap at the back, and the edges of the receiver will dig into your middle finger, so I added a curved Magpul triggerguard. Also correct would have been an A1 or A2 pistol grip, and while they look perfect on this gun, I’ve always hated the way they feel. They don’t have enough meat under the web of your hand. So, I went with a Magpul MOE pistol grip. When my hand is on the gun, you can’t see it, so the carbine still looks right.
Fully assembled as above, my Brownells 733 clone weighed 5 pounds, 6.7 ounces empty. With the stock collapsed, it is 27 inches long. With the stock fully extended, it is 30.5 inches long. It felt great, short, and light. The only question was whether the upper would be reliable and just how much recoil it would have, because it was so light. I was pleasantly surprised on both counts.
For testing, I just didn’t feel using polymer Magpul PMAGs would be appropriate, so for all of my shooting, I used GI contract aluminum magazines made by D&H, Brownells, and Colt (although they all had Magpul followers). I even used a few old 20-rounders (Colt and Adventure Line) with the original metal non-tilt followers that were ahead of their time.
To break in the upper, I put 160 rounds through it in less than 15 minutes, until the oil was smoking off the barrel (Winchester and Black Hills 5.56 and American Eagle .223 55-grain FMJ). I didn’t have a single problem. In fact, I was surprised at how little recoil this short, light carbine had. There didn’t seem to be any muzzle rise; the gun just moved around a bit in my hands when shooting.
For accuracy testing and to get a better idea of just what the muzzle was doing under recoil, I mounted a red dot on the 733. In my basement, I had an ARMS carry-handle mount with unusually-spaced slots (it pre-dates Picatinny rails standardized in 1994). I bought a Vortex 30mm Tactical low scope ring from MidwayUSA ($25) and installed my old Aimpoint CompC atop the gun.
You know what’s fascinating? Ultra-high mounts from Unity and the like are now all the rage on modern flat-top ARs … and that height is the same as what you get mounting an Aimpoint atop a carry handle. I used the 4-MOA dot of the Aimpoint for my accuracy testing, so if the groups are a bit bigger than you’re expecting, that’s why. With a magnified optic, I’m sure I could have cut them down quite a bit. While shooting, I discovered it wasn’t my imagination. Under recoil, the dot didn’t rise at all, just vibrated in place. Ejection was consistent, but the cases never landed much more than 6 feet from me.
The Aimpoint makes for a little faster shooting at distance, and it provides huge ’90s retro vibes, but I think I’m just going to stick to the iron sights for this gun in part because I know how to run iron sights fast at CQB distances.
I didn’t want to write this article until I had enough rounds through the Brownells upper to satisfy myself that it worked. Currently, I have 520 rounds through the upper, without cleaning, and only the lube that came on it from the factory. That includes 150 or so rounds of dirty steel case Wolf FMJ and SP, the only ammo that gave me visible flash in daylight. The only problem I had was the bolt not locking back on one of my ancient 20-rounders. On one range trip, I got the gun so hot that I couldn’t touch the carry handle. The heat has discolored the end of the barrel and the front sight post. But the upper just keeps purring along.
I love this build even more than I hoped I would. It is not as feature-laden as modern uppers, but Brownells’ 733 C7 upper is a bona fide piece of history, a callback to one of the greatest action movies ever made, short, light, fast, and fun to shoot.
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