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A Builder’s Guide to the M16A5 Concept Rifle

I want to be clear, there was never an official designation of the M16A5 rifle. The image in the cover of this very article is actually the Canadian C7A2. As much as I appreciate the design we’re talking about today, the M16A5 isn’t a rifle for clone dorks to obsess over. 

The US Marine Corps discussed the M16A5 concept circa 2013, and VLTOR put their version of it on display for a short time. But nothing came of it.

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The Marine Corps ultimately decided to field the M4 carbine across the service in 2015, and later the M27 IAR, killing any hope of the M16A5 actually coming to fruition.

Today, the “M16A5” is less about the proposed concept and instead colloquially describes any combination of 20” rifle barrel and collapsible stock.

The only known image of the short-lived M16A5 concept. Photo by SMGLEE

So why do I feel compelled to write this article? 

Just because the Marines chose not to field it doesn’t mean that the concept was invalid. In fact, the collapsible stock on a full-length upper is pretty common around the world. With this article, I’d like to walk you through some of the examples out there and share some pointers on building your own.

In the end, this configuration is extremely shootable. It’s one of my favorite rifles in the safe and works very well for a variety of tasks. To prove the point, it’s the one I chose to use in the NRA America’s Rifle match where I performed pretty well and was more hindered by my own lack of practice than the rifle itself.

History of the M16A5

Let’s talk about origins. The Marines were far from the first to toy with the concept of putting a collapsible stock on a full-length M16.

It wasn’t long into the fighting of Afghanistan and Iraq in the early 2000s before warfighters realized that a full-length rifle was less than ideal for urban fighting or riding around in vehicles.

You see, the M16 came about in an era of dismounted foot patrolling in expansive outdoor terrain. The troops wanted something more suited to their needs than the classic M16A2 and M16A4. 

There also weren’t enough M4 carbines to go around.

During the same period, the Canadians ran into the same conundrum with their C7A1 rifles.

By around 2011, both armies came up with a solution. However, they approached it in different ways.

The US Army AAL M-16 Hybrid Buttstock Kit

By 2009, many individual soldiers were unofficially experimenting with the collapsible buttstock configuration. United States Army Tank-automotive and Armaments Command (TACOM) started fielding requests for proposals to make it official. They created NSN 1005-01-569-6938 in 2008 for the project, but never officially announced it as an approved accessory until 2011.

TACOM authorized the hybrid buttock for any M16A2 or M16A4 in service. The Army apparently ran it through a 200,000-round torture test before approving it. 

The actual details are still locked behind approved access at, though.

M16 H6 Buffer hybrid buttstock authorization
Excerpt from PS 703, June 2011 declaring the new hybrid buttstock kit for M16 rifles as authorized for installation

The kit contained a standard M4 buffer tube, M4 stock, carbine spring, and specially-weighted “H6” buffer. Army units could purchase the kit for about $100 apiece for installation on their own rifles. 

The hybrid buttstock kit still required an armorer to install it. Furthermore, it was considered a temporary modification and any rifle with it had to be returned to its standard full-length configuration before returning to the armory at the end of a rotation.

The June 2011 edition of the Army’s PS Magazine, #703, announced the change. If you aren’t familiar with it, PS Magazine is the Army’s monthly publication about periodic maintenance practices. It’s loaded with good information. 

The image in the announcement, found on page 24 and seen above, looks suspiciously like a Magpul UBR. Don’t be fooled, though, the kit came with the standard M4 stock.

Army PS 771 discussing interchangeability of M16 H6 parts with standard carbine parts
Excerpt from Army PS 771 discussing interchangeability of hybrid buffer parts with standard carbine parts

In a later edition, #771 from February 2017, a weapons inspector wrote the editor reminding readers that the stock from the hybrid buttstock kit was not interchangeable with the standard M4 buttstock. However, interestingly, the authors of the magazine “misinterpreted” the letter and instead talked about the buffers not being the same.

If I was to guess, the “inspector” wasn’t really a gun guy and was only looking at the stamp on the buffer to decide whether the whole stock was correct. Confusingly, though, the associated image once again depicted a stock that looks like the Magpul UBR.

The Canadian C7A2

Before the US Army approved the hybrid buttstock with the H6 buffer, the Canadians were already ahead of the curve. Faced with the same problem, they took a much more direct path than initiating an expensive testing program and fielding a new buffer weight.

Canadian C7A2
Canadian soldier with the C7A2 rifle

Instead, they took the 4-position collapsible stock from the C8 carbine and stuck it on their C7A1 rifles with an H2 buffer. The new configuration was dubbed the C7A2. 

In truth, the upgrade was slightly more involved than that. Rather than considering the collapsible stock as a temporary modification, the Canadian military chose to have C7A1 rifles rebuilt at the depot level as they went back to Colt Canada for maintenance. 

This work included not only the new buttstock, but a new barrel, refinishing, a tri-rail adaptor at the front sight, and a few other elements.

Their original idea also included a KAC rail like the US M16A4, but they retained the plastic handguards as a cost-saving measure. The rifle also came equipped with the older ELCAN C79 optic, a predecessor to the SpecterOS found in my safe.

In all, Canadian troops took to the upgrade well. Though, like with the US military, the Canadian Army continues to steadily march towards issuing the 14.5” C8 carbine to everyone.

The USMC M16A5 Concept

That brings us to 2013. You see, both the US Army and the Canadians were already on the bandwagon with Collapsible stocks mounted to 20” rifles. Admittedly, the Canadians were more invested in the idea by turning it into a general issue weapon system rather than a temporary modification.

In January of 2013, Military Times’s Gear Scout blog published a blurb on a “unique” concept dubbed the M16A5 Armorer Conversion Marksman Rifle (ACMR) spotted at SHOT Show. The original article quickly disappeared, but the internet being what it is, the word quickly got around. 

Howard at Loose Rounds captured the important bits.

The M16A5 ACMR (Armorer Conversion Marksman Rifle) will be manufactured using components provided primarily by VLTOR Weapons System of Tuscon, Arizona, and this will be the largest contract ever taken on by the firm. VLTOR has previously been contracted to provide adjustable stock kits for the exist M16A4, and these kits have been well-liked and highly sought after. 

The ACMR will feature a monolithic rifle length VIS upper receiver and a VLTOR M16A5 adjustable stock kit, which provides a buffer tube with seven, as opposed to the usual six, choices of length of pull and uses the existing rifle length buffer and springs. All VLTOR parts will be provided in a Flat Dark Earth finish, per USMC request. 

The M16A5 eschews the carry handle rear sight but retains a fixed sight in the form of a Lewis Machine and Tool sight that replicates the sight common the M16 family of firearms and has been used previously by forces within the Navy Department on the Mk 18 CQBR. 

As the name suggests, upgrading an M16A4 to M16A5 spec will be a task simple enough for an armorer in-country, as the M16A5 retains the barrel, front sight, lower receiver, fire control group, bolt, bolt carrier group, gas tube, buffer and springs of the M16A4. 

Apparently, the USMC experimented with the Army’s H6 configuration but the commandant didn’t like it. They contracted with VLTOR to produce a product-improved M16A4.

The new concept had two primary differences.

The A5 Buffer System

First, VLTOR used their EMOD stock on top of their A5 buffer system. This tube was longer than the standard carbine tube but shorter than the full-length rifle version. It also included seven adjustment points for the stock. 

This intermediate-length buffer tube was ¾” longer than the carbine tube and intended to accept a full-length rifle spring rather than the carbine spring. Similarly, it also used an intermediate-length A5-buffer that had some unique internal characteristics.

AR Build Junkie caught up with Nick Wantland, head of Marketing and Sales at VLTOR to ask some questions about the A5 system. Here’s a short excerpt, but check out the whole interview at the link.

There’s a ton of things that it does simultaneously, some more nuanced than others…But the synopsis is it regulates carrier velocity, changes felt recoil impulse, and most importantly, it opens up the entire operational envelope of the gun. It allows the gun to run properly under a much wider range of input and factors. This usually equates to more overall reliability…which is a good thing.

The bottom line is that the use of a rifle-length spring alters the timing and recoil impulse of the system to be closer to that of a fixed-stock rifle.

In the end, that produces a smoother and more reliable weapon.

The Monolithic Upper

The other major change for the M16A5 concept was VLTOR’s use of a monolithic upper equipped with the newly-designed keymod interface. In 2013, the gun world was ablaze with monolithic uppers. 

The idea focused on improving rigidity and accuracy by having the upper receiver and rail all machined out of a single piece of aluminum. 

The VLTOR Monolithic VIS Keymod upper similar to that demonstrated on the M16A5 concept. Photo courtesy of VLTOR and Bauer Precision.

The idea was sound, but never caught on. There was the obvious hazard of damaging the rail meant replacing the entire receiver, but ultimately I think this time period in AR history was so full of innovation and “flavor of the week” accessories, as Howard at Loose Rounds put it, that people didn’t want to lock themselves into only one option. 

VLTOR still markets their monolithic upper system as the VIS.

Your own M16A5 Build

Now that you know the history, let’s talk about building your own. 

As I said earlier, the “official” M16A5 never came to fruition so there is no specific model to clone for yourself. That said, there are several concepts you can borrow from the design, as well as the Canadian C7A2 and US Army’s Hybrid Buttstock accessory. 

The moniker of “M16A5” really applies to any combination of collapsible stock with a 20” barrel.

The Barrel and Rail

So the first rule of this game is that you need to start with a 20” rifle upper. My own version uses a BCM 20” Government profile upper that I reviewed earlier. Really any 20” barrel will do, but I think a lightweight profile will balance better with a collapsible stock.

Something like the Faxon 20″ Gunner would work great here for a field rifle.

There is no requirement for a free-floated barrel here. 

The C7A2 uses the classic plastic handguards, and the Army’s H6 rifle came mounted on both the M16A2 and M16A4- neither of which was free floated. That said, there are some obvious benefits to giving yourself some rail-estate for accessories like vertical foregrips, bipods, lights, and lasers (if that’s your thing). 

Buffer System

The real business happens at the rear end. 

Both the US Army’s version and the Canadian model use standard carbine buffer tubs and springs. The Canadians use a standard H2 buffer while the US Army used a propriety “H6” buffer.

If you want to go the latter route, Damage Industries makes a commercially-available model.

Of course, the other path here is the VLTOR A5 system. That’s the most expensive “package,” though.

Since the M16A5 concept became widely known, a few more companies have jumped on the wagon. BCM makes their own intermediate-length buffer tube that’s compatible with rifle springs and VLTOR A5 buffers. The Magpul UBR 2.0 also grew in length to accept these components.

You can use a standard M16 rifle action spring, but I generally recommend the Sprinco “Green” spring as it has a longer life and just flat out works.

The Stock

Like many things with the AR-15, the stock you choose for your M16A5 is pure personal preference. The US Army and Canadian versions used the standard M4 carbine stock. VLTOR’s concept for the USMC had an EMOD. The PS magazine cartoon version seemed to have a UBR. 

So really, if you’re trying to be “correct,” any of those will work. 

Beyond that, really anything will do. Keep in mind that not all stocks will collapse all the way down to be flush with the receiver. I know my MOE carbine stock does not, leaving about a half-inch of space. My ACS and EMOD go all the way down, though.

As you can see in the cluster of photos above, I personally ran with an EMOD for a while before switching to the UBR 2.0. I find the extra weight of the UBR helps balance the full 20″ barrel a bit better than the EMOD did. Both work great, though.

Wrapping Up

So there you have it. This M16A5 build guide was fun to research. 

Even though I’ve had this configuration in my safe for a long time, I never really dug into its history at all. The collapsible stock on a full-length upper is one of my favorites to shoot, and I’ve run it in competitions and tactical classes alike.

Would I take it 100% of the time over something like a lightweight 16” barrel? Probably not. 

As much as I enjoy the 20” barrel, I have to keep in mind the tradeoffs with weight and balance. The configuration came about for a place and time as a way to offer just a little bit of help to warfighters who were not issued shorter carbines. 

If you have the option to use whatever you like, then this reason isn’t really a strong one for you. However, that still doesn’t diminish the fun of the configuration.

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Matt is the primary author and owner of The Everyday Marksman. He's a former military officer turned professional tech sector trainer. He's a lifelong learner, passionate outdoorsman, and steadfast supporter of firearms culture.

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Brent L Sauer

Great article Matt! I really liked the P.S. magazine references.


Back in 2010, I tried to push for an A4 upper on an M4 lower with an RCO(ACOG) before we deployed to Afghanistan. I wanted that muzzle velocity! My unit never authorized it, but I did play with the arrangement on some field ops and ranges and found it useful. Other Marines, not so much.

Replying to  Matt

My unit was a Field MP unit based in Camp Pendleton. We were given numerous mission profiles, and I had several billets. Notably we had no Designated Marksmen, but rather all the Expert qual’d marines were tasked with Guardian Angel tasks as they came up. Being handed a 14.5” over a 20” was less than ideal in my mind. I wanted the muzzle velocity that the 20” Boot musket offered, with the flexibility of the collapsible stock married to the best combat optic available to me. All of my higher Expert scores came from the A-4. During room clearing and… Read more »


Something interesting to note: The Canadian army has the C7A3/C8A4 project coming (slowly) down the pipe. For all intents and purposes, it’s looking like both of them will end up being variants of Colt Canada/Diemaco’s current Modular Railed Rifle (MRR) commerical offerings. Especially in the case of the potentially C7A3 it seems to be taking a forward thinking approach and using many of the best ideas and features on the market. the future C7A3 will likely have an 18″ free floated barrel, and monolithic M-Lok upper receiver, as far as it’s main differences over the previous C7A2. This seems to… Read more »


Great article.
Waaaay back in the day, some of us old guys put collapsible stocks on our M16A1s out in the Saudi desert. Worked great with the H2 buffers available way back then. The 20” gas system is pretty forgiving across a wide range.


I was an armor at fort stewart in 2001 when we got the new m16a4 for the 3rd infantry division. I called up TACOM on my post and told that would “modifiy” the weapon if I put a m4 stock on the m16a4.


Around the same time the kit became available, Fort Jackson added them to dozens of M16A2 rifles. They were issued primarily to petite female trainees who benefited from the reduced LOP while wearing body armor. They looked a little goofy, but all of them were reliable weapons.

Sam Falcon
Sam Falcon

As far as I know, when I took the USMC Combat Marksmanship Coach’s course, the M16A5 was considered to be similar to the M16A4 except that it comes with an adjustable stock, ambidextrous safety, and magazine release. That’s it.


It is completely false that the M16 came about “in an era of dismounted foot patrol”
The M16 came about during the height of the Cold War for use by heavily mechanized troops on the Central European Front.

It is an abject myth that the M16 is ill suited for operations in armored vehicles. It *does* suck for asymmetrical warfare patrols in HUMVEEs.
Signed, a former Mechanized Infantryman


Cool writeup. I’m a Marine (veteran) and didn’t even know that the M16A5 was ever almost a thing. As somebody whose primary AR is a 20″ BCM with collapsible stock and A5 system, I’ve always been the black sheep at shoots. But the thing just GOES, and refuses to stop, and man it’s hard to argue with the higher MV and lethality offered by a longer barrel. Kinda neat that a Marine vet ended up going with a faux M16A5 independently. Thanks for the writeup! Enjoying your blog. Keep it up.

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