Colt’s 901: Why Didn’t I Think of This?

CTD Staff Shoots CM901

Approved for release, Colt’s XM901 prototype is now hitting gun store shelves! It is now the CM901 if you’re military, LE901 if you’re law enforcement, or SP901 if you’re a civilian. This carbine takes modularity to a new level once thought impossible. Both .308 and 5.56 rounds can be fired using the same fully ambidextrous lower receiver. All the user has to do is switch complete uppers, insert the correct magazine, and start shooting. That’s right, the lower receiver of this gun accepts both Magpul .308 magazines (not the standard .308 PMAGS, however) and also the STANAG magazines used by .223 Rem/5.56 NATO AR-15s. How Colt accomplished this was a big secret and they hid it from the public until they received a U.S. Patent protecting their design. They would not let anyone photograph or video an upper receiver swap until the patent paperwork came back from Uncle Sam. This was wise, because Colt’s solution is so simple and elegant, every other AR manufacturer would have immediately copied it.

CTD Staff Shoots CM901
CTD Staff shooting the .308 CM901 at Media Day 2012.
LE 901 Mag Well Adapter
LE 901 Mag Well Adapter, thanks to The Packing Rat for this rare photo!
Here’s a photo of the 901’s mag well insert courtesy of The Packing Rat, a friendly California gun blogger who posts news and reviews from the Sunshine State at It is not complicated at all, just a sleeve that goes inside that big .308 mag well. I’m betting that right now there are bunches of other manufacturers who are slapping their foreheads for not thinking of that first. They will try to figure out a setup that gets the job done in a similar way without infringing on Colt’s patent. However, for the foreseeable future Colt is the only gun in town that can do this.

Colt moved the front receiver pin down and forward about an inch from its normal location on an AR-15. Designed specifically for the new system, the .308 upper simply uses the pin location. Using a standard 5.56 upper receiver, the lug for the front pin now holds an anodized aluminum magazine well insert, which has a new lug mounted on its front. This mates up with the 901’s new front pin location while the upper assembly slips onto the lower receiver. When the 5.56 upper and 901 lower come together, the upper’s mag well insert effectively shrinks down the magazine well to fit a regular 5.56 magazine. Colt bevels the inside of the mag well insert so it acts like a huge magazine funnel, like you would see on a custom 3-gun match rifle. Nice touch! One of our CTD staff members got to shoot a CM901 in .308 at SHOT Show Media Day 2012. He was very impressed with the balance and weight of the gun. Most .308 ARs are barrel-heavy beasts, but he reports that the 901 balances very nicely between both hands. Colt did a great job of keeping the overall weight down to just 9.25 pounds in the standard .308 configuration. He says that’s less than his competition 5.56 AR-15 weighs. With a 5.56 upper installed, the 901 weighs just half a pound more than a standard AR-15 with the same upper. Recoil was more than a .223 but not by much, and practical accuracy was excellent. Steel targets at 140 yards away rang out while shooting from a standing, unsupported position using only iron sights.

The first .308 SP901s are just now hitting the market, priced a little over $2,000. It’s the best technology and execution Colt can deliver, and they are making it available to us civilians at exactly the same time as they offer it to police and military units. That’s something that 2nd Amendment advocates can really appreciate.

Two SP901s
Front SP901 with 5.56 upper, rear SP901 with .308 upper.
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Comments (10)

  1. So, what’s the differences between CR, LE and SP? Is the CR full auto? LE a short barrel version? What’s the scoop CTD??? Colt’s LE Ar15s were eventually made available to the general public, will this hold true with the LE901?

  2. @Bob, there are plenty of AR type rifles that are available around $600. If you can’t afford a $600 rifle then maybe you should find a different hobby or a different line of work.

  3. Again the price is outside the average man’s range.I want to see a company come out with an AR type rifle that a low income wage earner can afford.

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