Black Rifles & Tactical Guns

50th Anniversary Colt Surprise

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By Holt Bodinson, GUNS Magazine

It’s the 50th Anniversary of the M16, and Colt is celebrating that milestone with the introduction of the most innovative AR platform ever developed—the dual caliber LE901-16S. Many have struggled with a design that would provide interchangeability between 7.62 NATO and 5.56 NATO utilizing one, common lower, but Colt has done it through brilliant engineering and design work.

Recently, a group of fellow writers and I had the opportunity to visit Colt’s Mfg. Co. LLC in Hartford, Conn. It’s one thing to write a review of a firearm. It’s quite another to be able to walk around the plant where it’s made and to be able to talk to the men and women who make it. To see raw materials being machined into finished products and to view machine tools, old and new, some dating back to the original run of the Model 1911.

There are actually two Colt’s. There is Colt’s Mfg. Co. LLC, which makes the complete lineup of Model 1911 pistols, including the Marine’s new M45 Close Quarter Battle Pistol, the new Mustang, the Single Action Army line, which once again includes the New Frontier model and the Colt Custom Shop, where the emphasis is on fine engraving and refinishing. You might call this the commercial side of the company, and it was recently injected with 10 million dollars of new capital to modernize its production and plant facilities.

The other face of Colt is Colt Defense LLC where a variety of models of M16 and AR-15 as well as M240B 7.62 and M249 5.56 machine guns roll off the line every day. In fact, Colt’s Mfg. Co. LLC orders its AR-15 sporters from Colt Defense LLC. Both companies are housed in the same plant but are more or less separated by a line on the floor so the same quality that is demanded under mil-spec contracts goes into every AR-15 sporter that leaves the factory.


Two qualities at Colt caught my attention immediately: a smart, switched on staff who are enthusiastic about regaining the leadership position the company once had and who are obsessed with listening to their customers about new product development; and a remarkable and overwhelming focus on quality control which includes a complete, in-house, chemical analysis of every batch of steel purchased and, for us AR lovers, a protocol to proof and Magnaflux the bolt and barrel together as a complete assembly that will stay together throughout the manufacturing process.

The new Colt 7.62/5.56 modular carbine was a revelation; especially considering it takes only a couple of minutes to make the changeover. The LE901 comes as a .308 Winchester (7.62 NATO) carbine with a 16.1-inch, chrome-lined barrel with a 1:12-inch twist and capped off with the highly effective Vortex flash hider.

The upper is machined from an aluminum forging to incorporate a monolithic handguard with full length, Picatinny (M1913) top and side rails. This 1-piece design is not only structurally rugged but also facilitates the use of a completely free-floated barrel for optimum accuracy. Attached to the inside of the monolithic handguard is a 180-degree heat shield at the 6 o’clock position underneath the barrel, designed to keep the shooter’s fore-end-grasping hand cool. The separate bottom rail can be removed, but I see no reason to do so.

The modern sporting rifle, in either .308 or .223, is ideal for varmint calling.

The modern sporting rifle, in either .308 or .223, is ideal for varmint calling.


Examining the LE901 upper in more detail reveals the first clue to understanding how Colt designed the switch-caliber carbine. The forward portion of the bolt carrier is massive to enclose the .308-size bolt, which features a spring-loaded firing pin by the way, but the rear of the carrier is the same diameter as that of an AR-15 bolt carrier. Ah-ha, eureka!

With its 5.56-dimensioned rear end, the .308 bolt carrier is now compatible with the diameter of the standard AR-15 lower receiver extension tube that houses the buffer and buffer spring, which is clue number two. To switch from a .308 upper to a .223 upper or vice versa, you must be able to change out buffers and buffer springs, and Colt’s innovative design makes that possible. Also, with its standard AR-15 extension tube, the LE901 will accept any mil-spec M4-type buttstock, although the stock, 3-position, Vltor Modstock is one of the finest ever assembled on a carbine. The Modstock is adaptable for quick release or standard slings, and each of its two side-battery compartments will house three lithium CR123 or two AA batteries.

The LE901 lower is machined with an AR-10 size magazine well to accommodate 7.62 magazines. Colt supplies two, polymer Magpul 20-round magazines with impact covers to protect the feed lips and prevent the lips from spreading when the magazine is stored fully loaded for an extended period of time.

The third clue to the design is the rear of the lower receiver is machined to AR-15 dimensions and features a standard AR-15 hammer, trigger and pistol grip. You can switch out triggers if you don’t care for the 5-1/2-pound single-stage pull on the stock trigger, and you can change out pistol grips and hammers.

One of the nice features of the LE901 lower is that the magazine release and bolt catch are ambidextrous. You can operate the essential controls from either side of the receiver, and again, through some clever design work, the magazine release functions with either 7.62- or 5.56-size magazines.

What we have here in the LE901 is a hybrid lower and upper with a blending of AR-10 and AR-15 features. To switch from 7.62 to 5.56, you need not only an AR-15 upper and a 5.56 buffer (identified with the stamped letter “H”) and an M4 buffer spring, you have to have some way of baffling the 7.62 magazine well so that 5.56 magazines fit perfectly. Colt developed the solution with the design of a captive AR-15 magazine well adapter compatible with any mil-spec AR-15 upper. This really is inspired engineering!

Swap Top

To change calibers, you remove the 7.62 upper and its associated buffer and buffer spring. Replace that buffer and buffer spring with a 5.56 buffer and spring. Seat a 5.56 upper with the 7.62 magazine well adapter in place on the LE901 lower, secure the upper to the lower with the front pivot pin and the rear takedown pin and go for it. It’s that simple—no tricks—no effort—and in 2 to 3 minutes, you’re back in business.
Because of the contours and the synthetic stocks of the AR, they’re hard to work on, even clean, without some simple but dedicated tooling. First and foremost, you need a magazine well vise, which fits inside the magazine well and supports the lower as you work on it or the upper. Battenfeld’s Wheeler Engineering “Delta Series” of tools is readily available and reasonably priced. In fact, they offer two complete AR tooling kits: an Essential Armorer’s Kit and a Professional Armorer’s Kit.

Pro Armorer’s Kit

I work with the Professional Kit because it contains all the tools I need to build, rebuild and tune the AR. At a minimum, I would recommend the following “Delta Series” tools: AR Armorer’s Vise, Maintenance Mat with exploded view of all AR Parts, Pivot Pin and Roll Pin Installation Tool, AR Front Sight Tool, AR Bore Guide, AR Adjustable Receiver Link, Bolt Carrier Brush, Chamber Brush and Magazine/ Upper Receiver Brush. More advanced “Delta Series” tooling permits you to change barrels, stocks and buffer tubes. The neat thing about the AR is that all you really need are hand tools!

Sights? The LE901 with its .308/7.62 upper is fitted with an elevation-adjustable, folding front sight and a flip-up, dual aperture rear sight adjustable for windage with the tip of a bullet. The Colt 5.56/.223 conversion upper features an elevation-adjustable, folding front sight and a Matech OGU83 flip-up rear sight that is windage and elevation adjustable and is factory calibrated for ranges from 200 to 600 yards in 50- and 100-yard increments. The Matech rear sight is currently the official US Army mil-spec sight for the M4 carbine and M16A4 rifle. The military expects the user to mount optical sights so both sight systems are referred to in military jargon as “Backup Iron Sight” or “BUIS.”

For optics, I selected Steiner’s military/tactical, close-quarter combat, 1-4x24mm scope for the .308/7.62 upper, mounted in a rugged, Burris 30mm “Proper-Eye-Position-Ready, AR mount fitted with Picatinny ring tops. The Steiner scope is supplied with their glass etched, “Rapid Dot” reticle mounted in the second focal plane. The reticle features a central, illuminated, red dot adjustable to 11 light levels and a range-calibrated, ladder reticle which at 4X conforms to the trajectory of the 7.62 NATO round from 100 to 700 meters. The scope is also available calibrated for the 5.56 NATO round.

The Steiner’s a brilliant scope. The elevation and windage adjustments are calibrated in milliradians. Each click is equal to 0.1 mRAD or 0.34 inch. If you think and operate in terms of mils, the adjustments are perfect. If you think and operate in terms of minutes-of-angle or MOA, the scope calibration values might take some time getting used to.

For the 5.56 NATO upper, I selected the unique, Nikon, P-223, 3-9×40 scope secured in a Nikon M-223 mount. The scope is fitted with Nikon’s BDC 600 range-compensating reticle. As supplied, the reticle at 9X is calibrated from 100 yards to 600 yards in 50-yard increments and is adjusted to the trajectory of a 55-grain polymer tipped bullet with a muzzle velocity of 3,240 fps.

The unique quality of the Nikon scope is that, if you are shooting an alternative loading (different bullet, different velocity), go to Nikon’s website, click “Spot On” on the toolbar and match the trajectory of the new loading to the existing reticle marks, which in the P-223 scope are a series of descending circles and hash marks.

How did the LE901 shoot? What I want to know is what is the inherent accuracy of a particular firearm. In short, what is the best level of performance this firearm is capable of delivering with the finest, proven ammunition available. After years of tough competition at the National Matches at Camp Perry, we know everything we need to know about squeezing the utmost accuracy out of the .223 Rem and .308 Win. On the basis of that experience, we have factory, match-grade ammunition readily available to us in those calibers, and refined, match-grade ammunition is exactly what I used to wring out the Colts. The pictured targets are illustrative of the results.

With Black Hills Ammunition’s .308 Winchester Match load, featuring a 168-grain HPBT at 2,650 fps, and Nosler’s .308 Custom Competition 168-grain HPBT load at 2,750 fps, the LE901 would hold 1 to 1-1/4 inches all day long with 3-shot groups at 100 yards. The LE901is a very pleasant .308 platform to shoot by the way—a bit loud but with minimal recoil.

With the 5.56 NATO upper installed, having a 1:7-inch twist, the LE901 would keep Black Hills Ammunition’s 52-grain HPBT Match load into 1 inch or less and Black Hills’ 77-grain HPBT Match load into 1-1/4 to 1-1/2 inches.

The LE901 combo is a real “keeper.” The only thing I will change is the trigger.

Colt’s on a roll with a consumer centric focus. Doug Campbell, Director of Domestic Sales, best summed it up when he said to me, “There has been a noticeable shift in the amount of new product development from Colt in the past year that was driven by a focus on the consumer market. Ideas came externally from our customers. We then leveraged the same Colt mil-spec quality that’s been used to fill military contracts for the past 10 years into an exciting array of civilian and law enforcement models. The LE901 is one of our most exciting new offerings.”

Yes, it is.

Thanks to the team at GUNS Magazine and to visit their site click here;

Black Hills Ammunition
P.O. Box 3090
Rapid City, SD 57709
(605) 348-5150


331 E. 8th St.
Greeley, CO 80631
(970) 356-1670

P.O. Box 671, Bend, OR 97709
(800) 285-3701

Wheeler Engineering Battenfeld Technologies
5885 W. Van Horn Tavern Rd.
Columbia, MO 65203
(573) 445-9200

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