Colt 6450 9mm Carbine

Colt 6450 9mm Carbine

It takes very little net surfing to find an extension of the perpetual caliber arguments: 9mm v. .45 ACP, .5.56 X 45 v. 7.62 X 39, and the list goes on and on. Accordingly, there is no dearth of arguments about the proper home defense firearm, or a firearm for any given purpose. Handgun, shotgun, rifle or carbine? Which caliber? Which specific cartridge?

I’ve never been a seeker for the perfect in any material thing. I don’t seek the perfect handgun or the perfect rifle or the perfect caliber of cartridge. I seek, instead, what works for me. I understand perfectly well that what works for and satisfies me may well not do the same for others, so I provide my perspective secure in the knowledge that others may accept, reject or modify it.

Left side receiver

Left side receiver

The little carbine at the top of this article is a modified Colt 9mm carbine. It’s a model 6450, manufactured in 2008. This, surprisingly, wasn’t easily discovered. There is no model number stamped on the receiver, but with the serial number and a call to a very helpful representative at Colt, it was quickly determined.

There are a number of rational reasons to own a carbine in the same caliber as one’s handgun, in my case, a Glock 26 in 9mm. Ammunition interchangeability is obvious, as is overall lower cost for a substantial supply of ammunition. As 9mm ammunition is plentiful–for the moment–and relatively inexpensive, it’s not difficult to be able to shoot enough to develop a high level of proficiency. A 16” barrel will also provide as much as 300 feet per second greater muzzle velocity and extend the useful range of the cartridge to 100 yards or a bit beyond with greatly enhanced accuracy potential. Particularly for urban–and most suburban–situations, that’s more than enough range, and there is really no such thing as too much accuracy. A properly configured carbine can make hanging such accessories as lasers and flashlights easier than one might expect, easier than with most pistols.

Ammo interchangeability is somewhat limited, however, by the fact that the magazines used by the carbine are not interchangeable with the 9mm Glocks I own and shoot. More about magazines later.

Absolute rationality, however, often must give way to more emotional concerns. I’ve always liked Colt AR variants–my primary .223 CAR-15 is an older Colt–and when I happened to spot this carbine hanging on the wall of my favorite local dealer, a bit of bartering and it was on its way home.

In its standard form, it has a standard AR carrying handle/rear sight, which somewhat limits optics and with optics, significantly raises the sightline over the bore. With a rifle intended for shooting at longer ranges this isn’t so much of a concern, but with a rifle intended for much closer ranges, that’s an issue. Remembering holdover at 25 yards and closer can become an annoyance.


Sharp-eyed readers will notice quite a few enhancements on the basic carbine:

L. Side Full

(1) Magpul MOE Commercial Spec. Stock. I prefer this stock configuration and use it on all my AR Carbines. It fits more snuggly than the original.  $39.95.  

(2) SureFire G2 Nitrolon flashlight. This is a lightweight and rugged light. There are far more powerful lights available–this is 65 lumens with a conventional rather than LED light source–but it works well at closer ranges and is inexpensive at $59.00 (I have seen this flashlight cheaper from a variety of sources).  

(3) VLTOR Scout Mount. This mount is relatively inexpensive, very well made, very easy to install and adjust, and weighs very little. $35.95.

(4) Daniel Defense Sling Mount. This is a simple and rugged single point sling mount that clamps to the tube behind the receiver and allows quick and easy detachment of a sling from the weapon. $75.00.

(5) LaserMax Uni-Max Value Pack for Rifle. More on this in the text. $199.00

(6) Yankee Hill Machine Lightweight Series Carbine Forearm. $134.00.

(7) Yankee Hill Machine Forearm End Cap. $22.00

(8) Yankee Hill Machine 5C2 Compensator/Flash Hider. $34.00

(9) Yankee Hill Machine Upper Receiver.  $122.00

(10) Bushnell 1X MP Red dot sight. $159.00 According to several sources, this sight has been discontinued, but it is still available from a varity of sources including Amazon. com.

(11) Magpul MBUS Rear Sight. $57.95

(12) Magpul MOE Polymer Trigger Guard.  $8.95

In researching flat top receivers, I chanced onto Yankee Hill Machine and I’m glad I did. Their prices for forearms include installation. The entire process took about two weeks, and most of that time was shipping both ways. While I was getting the new upper, I decided to have one of their excellent free floating forearms installed as well as a forearm end cap and flash hider. The design, quality of manufacture and service are exemplary.

The Bushnell MP red dot sight has apparently been discontinued, but it works very well. It features a T-dot reticle and red and green modes. It is very robust and reliable. It was easy to sight in and has reliably held zero. My only complaint is that it’s a bit heavy, and for that reason alone, I’m considering a replacement, but it certainly works well, and I’m sure one can be found in a variety of places, likely at considerable discounts.

I also added the excellent Magpul MBUS rear sight. This is a polymer flip up design that is inexpensive and unobtrusive. The flip up feature is secure–very unlikely to be triggered accidently–and positive in function, and the rear aperture appropriately sized and clear. One never knows when a battery will go dead or an electronic sight will malfunction.

The Magpul trigger guard was more or less a “I saw it on the dealer’s wall and it was inexpensive, so why not?” purchase. The original Colt trigger guard folds sort of flat against the handgrip for Arctic conditions, but in reality, I’ll probably never face that kind of environment, and the Magpul product enlarges the trigger guard sufficiently to nicely accommodate gloves.

The flash hider promised slightly more efficiency, and its design might cause some damage if used to jab an assailant at close range.  Using any AR-carbine or rifle with a bayonet or as an impact weapon is never a good idea.  They’re so lightly built blows powerful enough to cause damage to an opponent are also very likely to cause serious damage to the weapon.

R side full

The Laser Max laser and package are rather neat. Because I do not shoot any of my AR carbines enough to develop an automatic habit of using Kentucky windage to compensate for the high sight line at shorter distances–I really have to think about it–I decided to install the laser. The package includes not only the laser unit, but a substantial momentary activation pad, a heavy duty polymer sheath into which to insert it, and several clips for cord control. The polymer sheath actually prevents the heat generated by longer activations from bothering the fingers, but still allows positive activation. Rather than use the clips, I chose to use a few small cable ties. They’re lower profile and less size and weight.  The laser and sheath/cable clamps can also be purchased separately.

The laser unit is a Laser Max mainstay, and despite being larger than some on the market, is very light and robust. There is much to recommend a slightly bigger unit, as anyone that has had to wrestle with tiny lasers and their equally tiny allen wrenches and adjustment parameters can attest. Battery changes are quick and easy and do not affect zero. A constant on, or pulse, mode may be selected.

One of the drawbacks of red lasers is in bright daylight they’re not always easy to see beyond 15 yards or so. In pulse mode, that distance is extended. With this unit, I have the red dot sight for beyond 25 yards, and the laser for closer ranges. One of the problems of laser sights with handguns is the handgun must essentially be aligned properly on target in order to see the laser. That process is easier with a long gun.


The 9mm carbine differs from the .223/5.56 version in several significant ways. Because it is a blowback rather than a direct impingement gas action, the bolt is significantly different. A standard .223 bolt is on the left, the 9mm carbine bolt on the right.

Left: .223 bolt/bolt carrier Right: 9mm bolt

Left: .223 bolt/bolt carrier
Right: 9mm bolt

Notice that the 9mm bolt has no gas key, though a similar structure is staked in place. I suspect this is not only to help keep the bolt properly oriented in the receiver, but also adds necessary weight. Rotating locking lugs are unnecessary, and the 9mm bolt’s configuration is also quite different. I didn’t weigh them, but the 9mm bolt does feel noticeably heavier than the standard bolt.

Unsurprisingly, this makes the 9mm carbine considerably easier and less time consuming to clean, and not nearly as Q-tip intensive. I don’t mind gun cleaning and do it with dedication, but it’s nice not to have to spend quite so much time.

Top: .223 Bottom: 9mm

Top: .223
Bottom: 9mm

Magazines are considerably different. Loading the 9mm magazines takes considerably more force, and loaded, they feel substantially heavier than a loaded .223 magazine, which, considering the generally much greater weight of 9mm bullets, is hardly surprising. Unless one has very robust thumbs, a loading tool is a very good idea. By the time 20 rounds are loaded, loading the remaining rounds becomes more a wrestling match than a pleasure. I’m using Pro-Mag magazines and have found them to be robust and reliable. I did try to find 20-round magazines–they would have made sighting in and bench shooting easier–but none that I could obtain would actually fit the Colt. The latch points on the magazines did not align with the Colt magazine catch.

Also noticeable is the much greater length of the 9mm magazine. Taking a very low prone position is much more difficult with the 9mm carbine.

Mag Well

Notice the polymer insert in the magazine well. It is held in place by two pins, visible in this and several other illustrations (including below). Magazine insertion and release is no different from a .223 carbine. All of the controls are identical in size, configuration, function and position, and the 9mm carbine breaks down and reassembles in the same way as .223/5.56 carbines.

Right side receiver

Right side receiver

Several other differences are the polymer brass deflector and the shortened ejection port cover. The ejection port cover tended to hang up a little on the polymer deflector, but a few strokes with a Dremel tool solved that problem. Owners of similar carbines have reported that the polymer deflector isn’t strictly necessary, and I suspect they’re right, but it doesn’t hurt anything, and replacing it would also require replacing the cut down ejection port cover with a standard item, so I haven’t bothered.

The forward assist plunger is retained, though it’s unlikely to be necessary.


The balance of the 9mm carbine, though equipped identically to my Colt AR carbine, is slightly different. It is obviously a bit heavier. Not uncomfortably so, but heavier nonetheless, the center of gravity a bit more toward the butt.

The recoil is actually greater than a .223 carbine, as counterintuitive as that might, at first, seem to be. This is, after all, an 8+ pound carbine firing a pistol cartridge. How could it recoil more than a carbine firing an intermediate rifle cartridge? This is primarily because the .223 version uses a gas action, which is famously gentle in shooting.  The weight of the respective projectiles likely plays a role in perceived recoil.

Firing the 9mm, one feels more of a backward push, and slightly more muzzle elevation. This is, I suspect, more due to the greater mass of the 9mm bolt, even though it moves a shorter distance due to the shorter cartridge. Gas actions really do tend to soak up some of the recoil impulse. I suspect the speed/duration of the cycling of the actions differs as well, but I have no way to reliably quantify that observation. It certainly feels like there is more going on inside the receiver, and it seems to take perceptibly longer. One might say it doesn’t feel as smooth and refined as a .223.

I don’t mean to suggest that the 9mm is difficult to shoot. It’s still a pistol cartridge being fired in a carbine. It is, however, different than shooting a .223 AR. It requires a slightly different technique, and perhaps a bit more forward weight shift. It is still easy to put multiple rounds on target in rapid fire, and is not in any way disturbing or painful.

Ejection is positive and energetic, tossing expended brass some 8-10 feet away.

Accuracy out to 100 yards is a bit less than one can expect with .223 ammunition. Putting multiple rounds into a 5” circle at 100 yards is not at all difficult, even off hand, but the limitations of the cartridge at that distance do not make the carbine a tack driver. I’ve fired it at 200 yards, and groups can open considerably, depending primarily on the brand of ammunition and the bullet configuration. Full metal jacket ammunition tends to be more accurate at that range, which is also unsurprising. By “considerably,” I mean that keeping every round on a standard silhouette target is not terribly demanding, but a bit of Kentucky windage is always required, and wind has a great deal more effect. I don’t have velocity figures, but I suspect the bullets are traveling at quite a bit less than standard pistol muzzle velocity at that range.

At closer ranges–50 yards and less–accuracy greater than can be expected in a pistol is routine. Carbines, because of their longer sight radius, greater weight and stability and longer barrels have greater accuracy potential than handguns chambered for the same rounds.

Having fired a variety of 9mm carbines, including fully automatic models, the Colt’s accuracy is certainly representative of the class.


Recent news articles suggest the Colt may find itself in bankruptcy trouble. If so, that would be a tragic chapter in the history of American firearms. But anyone seeking a 9mm carbine can find models from a variety of other manufacturers. The Truth About Guns, kind enough to regularly publish me, recently posted an article on the JR Enterprises GMR-12 carbine, which uses standard Glock magazines. It would probably not work with short, ten-round Glock 26 magazines–that’s my daily carry gun–but Glock 19 and 17 magazines would surely work, as would the 32 round Glock magazines depicted in the article. It’s not a cheap rifle, but for those that prize magazine interchangeability, it could be a selling point.

My Colt is reliable, accurate, and fun to shoot. Its magazine capacity, relatively light weight, and excellent ergonomics make it suitable for a variety of roles. What more reason does one need to buy a firearm?