Gun Review: Colt 901 LE901-16S 5.56mm And 7.62mm AR-15

Colt 901, with 6920 upper and magwell conversion

Top: Colt 901 in .308/7.62mm Below: Colt 6920 5.56mm upper with conversion parts to fix onto the 901 lower

I’m really not an AR sort of guy. Sure, I’ve handled and shot a bunch of them, but they never really jumped out at me as really cool guns. Probably because they are the most popular rifle design in the US, and I tend to be more interested in the weird and obscure. So I have to admit that when I learned that Colt was sending me a Model 901 to review, I had to check the ‘net to find out what that was…

Initial Expectations

Well, when I did learn what I was going to be shooting, I got rather excited – the 901 looked like just about everything I would want in an AR, if I were to get one. First off, let’s mention the big point: it’s a .308 AR that can use standard AR-15 upper assemblies. That means you can use a 901 lower with all the 5.56mm uppers you already have, and with all other standard-size uppers as well – 5.45x39mm, .22LR, 5.7x28mm, .458 SOCOM, .300 Blackout, and so on. There have been other AR designs to offer this interchangeability between long and short cartridges, but Colt’s solution to the problem appears to be the simplest (and by extension, best) yet. It is certainly more efficient than the companies offering modular lowers – with the 901 you only need the one magwell spacer that comes with the gun, and you can run any upper without buying anything else.

I also saw that the 901 is fitted with a free-floated barrel and monolithic upper for maximum potential accuracy. It actually comes with iron sights, and pretty good ones at that. It has (almost) fully ambidextrous controls, which is great for lefties like myself. Despite having a not-military configuration, is comes with a Vortex flash hider and a bayonet lug. I don’t have any real use for the bayonet lug, but it strikes me as a thumb in the eye of the gun-banning crowd, and I like that. So – I’m liking what I see.

Colt 901, with 6920 upper and magwell conversion

Top: Colt 901 in .308/7.62mm
Below: Colt 6920 5.56mm upper with conversion parts to fix onto the 901 lower

The review package I was expecting from Colt included a 6920 standard 5.56mm upper receiver as well as the complete 7.62mm rifle, and the additional parts required to swap between the uppers (5.56mm-weighted buffer and magwell insert). So with some excitement built up and expectations set, I sat back and waited for the rifle to arrive. Colt was probably going to get back a gun with some scuffs and scratches…it won’t be easy for an AR to really impress me.


The ideal firearm controls are naturally ambidextrous without needing to be mirrored – like the M1 Garand’s safety. The AR design was designed with right-handed controls, though, and ambidextrous is a selling point today. Not because it’s really all that important – a practiced lefty will not be hindered by the normal controls – but because folks like to have the extra stuff on their guns…”just in case.”

Anyway, on the 901 Colt decided to add in left-handed controls for the bolt release and mag release. These aren’t mirrored duplicates of the standard controls, but they are basically functional duplicates. The added size of the .308 lower gave them some space to use, and they did so. The lefty bolt release (which does not also function as a manual hold-open) sits between the trigger and the brass deflector. It’s a perfectly functional paddle – smack it to drop the bolt – and it works just fine. The original right-handed one is a bit easier to use, because it is the highest element on that side of the gun, so you can kinda slap blindly at the receiver and have a decent chance of hitting it, while the lefty one is a bit protected by the brass deflector. But that’s a pretty trivial issue.

Left-handed bolt release on the Colt 901

Left-handed bolt release paddle

The lefty mag release is a lever positioned at the bottom rear of the magwell – not a higher-up button like the original right-handed one. To understand where the lefty one is, imagine indexing your (left) trigger finger straight out onto the magwell to stay off the trigger. Where your finger lands on the magwell is exactly where the mag release sits. It’s easy to reach from a firing grip, but I expect that sooner or later I would use it to unintentionally dump my magazine while transitioning between targets or running from one shooting location to another in a match. It’s a tradeoff – you get to drop mags with your firing hand (as a lefty), but you’ll need to train yourself to index your trigger finger somewhere different to prevent accidental unloading.

Left handed mag release on Colt 901

Left handed mag release on Colt 901 – right where my trigger finger rests

The lefty safety in the AR world is the simplest of the ambi controls…and that makes me wonder why the 901 doesn’t include one. All the work that went into the bolt and mag releases, and they didn’t bother to include a mirrored safety? Huh. The photo on Colt’s web site does show an ambi safety, so maybe they just neglected to put it on the review model? At least that’s an easy part to retrofit yourself if you want it.

The trigger Colt uses in the 901 is a standard military style one – single stage and a bit gritty. I’m sure it was easy and convenient for Colt to use, but it’s not up to the standards of the rest of the rifle’s spec sheet. Any serious shooter will find themselves wanting to replace it with a better one. Fortunately, it is 100% AR-compatible, so any standard replacement type will drop in.


The 901 comes with a standard basic A2 pistol grip, which works just fine. If it’s not tactical enough, you can put on whatever other grip you prefer. The stock is a 4-position Vltor unit with storage space for spare batteries. It does everything a stock should, without going over the top.

The front handguard is a free-floated quad rail, so you can mount all the lasers, IR strobes, bipods, tactical illuminators, front grips, sling swivels, and coffee mug holders that your heart desires. Of course, if you just want to put on an optical sight (or, inconceivably, nothing at all) you’ll need to add on some rubber rail covers so it doesn’t feel like grabbing a cheese grater. And you get the added weight of having a quad rail whether you use it or not. The foreend does include mounting points for the included very nice sling swivels at the front and back of the side rails on both the left and right, which is nice.  Between those and the mounting points on the Vltor stock, you can have pretty much any sling configuration you want (unless you want to use a 1903-style shooting sling).


In the early days of commercial .308 ARs, magazines were a real issue. It seemed like they were all proprietary and expensive. Well, Colt recognized that people want cheap and available mags, and they designed the 901 to use the .308 mags made by Magpul (which are interchangeable with Stoner SR-25 mags). These are durable, easy to find, and relatively cheap (about $20). Outstanding!

The magwell spacer used to convert the gun to use a 5.56mm upper works well with aluminum GI mags, steel HK mags, and polymer Magpul mags (in short, everything I tried out). They all load smoothly, and drop free when released (as do the .308 mags, I should note).


Colt’s design for allowing the use of standard 5.56mm-sized upper assemblies on the .308-sized 901 lower is both clever and simple. It consists of a single part, an aluminum magazine well spacer that shortens and narrows the magwell to the size of a 5.56mm magazine. This spacer has a captive flush pin that attaches it to the front takedown pin hole on the 5.56mm (or any other standard configuration) lower. The spacer then has a second hole in it which lines up with the front takedown pin on the 901 lower. All you have to do is snap the spacer onto your upper, and it will drop onto the 901 with no more hassle than putting it on any standard AR lower. While using a 5.56mm upper, this pin holding on the spacer is captive inside the .308 magazine well, and cannot work loose or fall out.

Colt 901 magazine well insert for using standard 5.56mm upper assemblies

Magwell conversion spacer for mounting a standard upper on a .308-size 901 lower.

There is one other detail that needs to be addressed for this sort of modularity. The 5.56mm and .308 cartridges require different buffer weights and springs (as do many other caliber conversions). The buffer tube on the 901 is the same size as a standard AR, so you just drop in the appropriate buffer and spring for whichever upper you are using (the 901’s buffer is helpfully stamped “308” to avoid confusion). The .308 bolt carrier for the 901 is also reduced in diameter at the rear so as to fit into the buffer tube.

What makes this design particularly appealing is that unlike the modular lowers that some companies have, this setup is totally non-proprietary. The magwell spacer will fit any standard upper, whether it’s made by Colt or any other company. So you can use the 901 lower as a .308 rifle, or anything else from a .22LR trainer to a single-shot .50BMG.


The Colt 901 is obviously intended to have some sort of optic mounted, in order to really exploit the potential of the 7.62x51mm cartridge. The full-length top rail makes that easy to do. Still, most of my own gun collection was designed before the 1913 rail was, and I don’t have much of that newfangled optical stuff floating around to test with. So I did the unexpected and shot the 901 using just the iron sights it came with. The front sight is integral to the gas block, and folds down when not in use (so it doesn’t interfere with your optical sight picture). The rear sight is a Colt flip-up model, with a huge ghost ring for up-close use and a much smaller aperture for longer, more precise shooting. It is adjustable for windage with a nice click system. Elevation is adjusted by raising or lowering the front post (which is square; cool).

Colt 901 factory rear sight

Colt 901 factory rear sight – very nice for a backup style

The irons were very nice to use. The factory zero didn’t require any adjustment, and I like the size of both the apertures.


I didn’t shoot the 901 for groups on paper. Frankly, there are much better shots out there who have done that with this rifle, and they’ve all found it to be excellent. I think we all know that a Colt AR will shoot better than 95% of the people who will buy it (myself included!). I’m more interested in practical accuracy – how well do the sights, trigger, barrel, and other elements of the rifle come together to give you groups when shooting from field position? So, I handed the 901 (with the 6920 5.56mm upper) off to my girlfriend and headed to a 2-gun action match. She is only an occasional shooter and had never shot an AR before, and I figured this would be a good test of what the non-tactical-expert can expect from the Colt 901.

The long(ish) portion of this particular match had us shooting full, 1/3, and 1/4 sized silhouettes from 175 yards, off roof props, through windows, and lying in eroded gullies. She made more than a few first-round hits on the smaller targets in those circumstances, and I think that says everything that needs to be said about Colt AR accuracy. It’s excellent.

I should also mention, for those who haven’t look at Colt’s spec sheet, that the .308 upper uses a 1:12″ twist, a 16.1″ heavy barrel, and a Vortex flash hider. The flash hider is an excellent one, any only needs to be replaced if you value looks over performance.


(cue ominous music)

To steal a line from a friend of mine, the AR-15 is like a helicopter. When everything works, it can do some amazing things – but it only takes one tiny thing going wrong to give you Blackhawk Down. This (IMO) largely explains why there is so much controversy about AR reliability – lots of people have taken the time to buy or build high quality ARs where everything works right, and lots of other people have bought or built iffy guns with tolerance stacking problems or small defects that cause them to malfunction at the first sight of dirt. One would naturally assume that Colt – the original military M16 manufacturer – would have a proper idea of how to make a flawless AR.

For the price tag of the 901, I would actually take it for granted.

As part of my testing and evaluation, I grabbed an extra .308 P-Mag (the rifle shipped with one) and headed out to a Competition Skills Course offered by Russell Phagan. It was a class teaching the various rifle skills specifically applicable to multigun competition, and had me shooting offhand, from platforms, rollover prone, through pieces of pipe, and other less-than-standard positions. I went through about 100 rounds of surplus South African ball ammo (brass cased, noncorrosive – good stuff that will run all day long in my M1, 1919, and every other .308 I’ve owned), had no fewer than three malfunctions.

Two of the malfs were failures of the bolt to cycle far enough back to pick up a new round from the magazine, resulting in an empty chamber, a click instead of a bang, and a need to manually charge the rifle. The third malf had the bolt push a round halfway out of the magazine before stopping, which required a slightly more involved clearing procedure.

Shootings the Colt 901 at a competition skills class

Shooting right-handed around a barricade, as a lefty. Immediately prior to this photo, I had 2 malfs in less than 10 rounds.

Colt did send a replacement upper when I notified them of this issue, and that replacement runs flawlessly. I was not the first gun writer to be sent this individual rifle for review purposes, and it may have been damaged by previous reviewers, or it may have just been poor QC.

On paper, the 901 is outstanding. Whoever came up with the spec sheet did a great job – they checked off all the right boxes. Vortex flash hider, Vltor stock, Magpul magazines, ambi controls, monolithic upper, quad rails for all your extra widgets, good backup iron sights, and of course the .223/.308 modularity. Using the second upper they send, the rifle ran flawlessly, and much better shooters than I have found the gun’s accuracy to be outstanding.

So is it worth the $2400 price tag? If you want the caliber and action-length modularity, then yes – it’s definitely the best option out there. I would just make sure to give your rifle a thorough inspection when you receive it, and have any problems addressed right away. Colt will make good on any problems – it’s just a shame that they would need to.

Ian McCollum

Ian McCollum lives in Arizona, where he spends his time searching out rare, unusual, and experimental firearms for his daily blog at His shooting background is in bullseye pistol, and before becoming a full-time gun writer he worked in the solar power industry.


  • allannon

    How would the mag well insert work with a standard AR-10 lower? The BCG is nonstandard, but is that a requirement or a design choice by Colt?

    Being able to use any standard upper is nice, but being able to eke a bit of flexibility out of any AR-10 would be attractive.

    • Esh325

      There is no such thing as a “standard AR-10 lower” to my knowledge. Each one has different specs. It’s unfortunate .308’s AR’s didn’t get the interchangability the AR15 did.

      • Joshua

        This Colt lower will be the standard soon as it is built around Magpuls 308 magazines, something alot are starting to take into account when making 308 AR rifles.

        • Esh325

          I think its patented.

    • Guest

      It wouldn’t work with a standard AR10, because that lower would not have the attachment point to hold the spacer in place.

    • I don’t believe it would. Specs tend to be different for AR10 lowers. Not much but enough.

      • Garrett


        The Colt 901 lower has a different pin position for the front. It sits much lower compared to ALL other AR10 designs. The conversion block is proprietary to the ‘901.

  • iksnilol

    They should have used a 18 inch barrel. .308 has a big flash with anything less than 18.

  • nndj25

    Great review, but does it have a low shelf to accept a DIAS? Are the .223 and .308 carriers semi or full-auto? This would be a neat way to use a DIAS for .308 if it worked.

  • 11b

    Ian McCollum! I love Forgotten Weapons, glad to see you writing here! Keep up the good work.

    • Yep he’s been here some time now. Glad to have him:-)

    • st4

      Agreed. Always waiting for a new video to pop up on his channel!

  • DiverEngrSL17K

    Great review as usual, Ian, with many thanks — it’s always gratifying to see such an honest, thorough, no-nonsense perspective based on hard facts that gets past the usual biases and skewed opinions one tends to see in a lot of other presentations.

  • MZupcak

    We don’t need more direct impingement systems and buffer tubes! I’ll be sick if the US armed forces adopt this over something like the SCAR just because you can swap uppers. I don’t know what kinds of people Colt has working on their designs, but they seem to assume that the American government and civilians will buy whatever unimaginative, mediocre pile of overweight metal they produce just because the ghost of Samuel Colt tells us to. It’s time to admit that, while the DI Stoneage System has become synonymous with the American military, there are better options available for a weapon of war.

    • ColaBox

      I wont deny that there are better firearms for warfare, and I wont even get into what I think about the SCAR, but there’s nothing wrong with DI and buffer tubes. Hard to get dirty and easy to clean. Hell, my STAG can eat Wolf like a fat kid eats cake, wipe wipe wipe, trickle some oil and its ready to go another 1000 rounds of cheap crap. Piston and free float are the new firearm trend these days and both are a half baked marketing idea at best IMO. Just because HK did something doesn’t mean its gold.

    • J.K.

      Drinking the koolaide is fine, but stop spreading chairborne ranger FUD.

      • MZupcak

        Chairborne? I love it! I am an “armchair commando”, no question. I’m also an AR piston fan but not because of HK. In fact, I like LWRC better. I like the idea of the piston because it allows more rounds to be fired in between cleaning. In dirty environments, piston guns have been shown to have fewer malfunctions (or maybe you think those US Gov tests were set up to favor HK)
        As for buffer tubes, they don’t allow a true folding stock. What AAC did with the super-short buffer tube and retractable stock on their “Honey Badger” isn’t a bad compromise, though. In fact, that stock setup might be the sickest thing I’ve seen for the AR in a while. If Magpul started making stock kits like that, I expect they’d make a killing on them. No pun intended.

        • bb

          I thought the XM8 exceeded both the 416 and SCAR, so wouldn’t that make more sense to adopt? In spite of that, the US Gov chose no upgrade at all. I’m more in favor of the ACR type program of the late 80’s with more radical ideas than simply plastic-fying 1950’s tech.

    • There are way no many points to address in answering your comment. For the government spending that much money to change over to something like a SCAR would be more than they could afford in good economic times.
      Also there’s nothing wrong with the DI system. I’ve never had a problem with one since I started shooting AR’s in the late 70’s.

      • MZupcak

        I see the point you’re trying to make but I don’t completely agree with the financial argument. Compared to the rest of our military expenditures, rifles might as well be free. We have about 68,000 troops in Afghanistan. To equip every single one of them with a SCAR-H or -L, even at $3k per rifle (steep for a US Gov contract), would cost just over $200M (less than 1/10th the cost of a single stealth bomber). Not to mention the old M4s could be donated to cash-strapped city/county LE organizations or even allied troops.

        • st4

          Unless the next-gen rifle provides a substantial increase of a fighting advantage ie. 95 round magazines of “10mm explosive-tip caseless,” or, “phased plasma rifle in da fourty watt range,” I’m not interested in contributing my tax dollars towards it. 😛

        • The problem is they don’t just purchase the rifle. They also pay for factory support for a period of time as well as a ton of parts and on and on. The cost per unit with these extras will run in the $6000 range.

        • RocketScientist

          As for the cost of an upgrade, Its like Phil says. But to his list add training, and completely replacing the entire infrastructure that exists to support the AR-pattern rifles currently in use (weapons racks, armorers rests/jigs, educational/training materials, blah blah blah, the list goes on). We’re talking 100’s annd 100’s of millions of dollars for at best a marginal (non-existant?) improvement. Doesnn’t make practical/fiscal sense at this point.

          • MZupcak

            You and Phil W make good points. I didn’t think of many of those things.

    • tfb.lurker

      I could have swore this was a Lance comment at first.

    • Andrew

      Oh look, another Piston Puffer.

    • Joshua

      You cannot just swap the upper on the SCAR. we have the 5.56 conversion kits in the system and there is more to it than just an upper.

      There is also a reason why no one I know brings the SCAR out on patrol, we all bring our M4A1’s and CQBR’s. Frankly the SCAR is a crappy weapon that performed horribly in field trials and still has numerous issues to this day.

    • Ian McCollum

      Don’t worry; the US military will not be adopting this, or the SCAR, or any other new rifle in the foreseeable future. The cost of changing away from the M4 is wildly out of proportion to the miniscule benefit that might result.

  • ColaBox

    Wouldn’t say its the most popular weapon in the US but definantly the most talked about.

  • Mark N.

    If I were to ever own an AR, this sort of interchangeability of uppers would be a very desirable feature. Does Colt make this in a CA compliant version?

  • mechamaster

    I hate to admit that only gamer of COD 3 know this Colt 901 things ( in 7,62x51mm version )

  • Sid

    Good review. I just don’t see the need for the design. A common lower is really not saving money. The uppers are nearly the cost of the entire rifle. With the exception of .300BLK, there working parts of the rifle are not compatibale across the calibers.
    Point being – a common lower is not really that useful. I hope users enjoy it. Glad it is an option. It just does not seem to be very practical.

    • Cymond

      It makes a bit more sense for people who use expensive accessories. You can easily spend $400 per lower on upgrades, so I can understand why people would prefer to minimize the number of lowers in their collection.

  • Nick

    While I was reading this, I saw the picture of you shooting and thought to myself, “man that guy looks familiar…” I got to the bottom and checked the author, now I know why! I love your youtube channel and blog! Somehow I haven’t seen any of your articles on here though. Great write up, and I’m glad to see you on TFB!