Build an AR-15: Choosing the Right Butt Stock

THE SERIES

• Part 1: Build an AR-15: The Series Introduction
• Part 2: Build an AR-15: AR Calibers
• Part 3: Build an AR-15: Direct Impingement or Piston Operation
• Part 4: Build an AR-15: Tools and Materials
• Part 5: Build an AR-15: The Lowdown on Lowers
• Part 6: Build an AR-15: Intro to Uppers
• Part 7: Build an AR-15: Barrels
• Part 8: Build an AR-15: Choose The Right Buttstock 
• Part 9: Build an AR-15: Choosing the Right Optic

When it comes to choosing the right buttstock, we’ve got good news and less good news. The good news is that there are hundreds from which to choose. The less good news is that figuring out which type will work on your rifle is just a little bit complicated. No worries, we’ll start this article with a quick overview of the four (not including AR pistol) types of buttstocks and mounting systems.

Actually, there’s more good news. Not only are there may brands from which to choose, but there are also plenty of mission-specific designs. Want something really adjustable for setting up a precision AR? No sweat. How about one that looks as bad@ass as the rest of your custom built rifle? Piece of cake, there are plenty of innovative designs out there.

Oh, the last piece of good news is that once you figure out which parts go with which other parts, installation is really easy.

But First…

To mount the stock, you’ll need to make sure you have the receiver extension (buffer) tube, buffer, recoil spring, receiver plate and locking ring installed. Read on to make sure that these parts, sometimes known as the mounting kit, are compatible with your butt stock of choice.

What Type of Stock?

There are four “classes” of stocks for AR-type rifles, so you need to make sure that the stock mounting parts (receiver extension tube, recoil spring, and buffer) are compatible with the butt stock you want to use. The easiest way to ensure blissful coexistence between these parts is to choose your butt stock first, then order the appropriate mounting parts. If you already have the receiver extension (buffer) tube, etc., then you just need to order the correct variant of your butt stock. Many aftermarket stock vendors offer multiple “sizes” of butt stocks for any given model.

Let’s take a look at the four basic classifications of AR stock systems.

A1 Rifle

If you were in ‘Nam or have watched movies about the ‘Nam, you’ll recognize the original fixed stock M16A1. It’s that big, one-piece triangular one. The Army intended it to fit a wide variety of shooters firing from combat positions, meaning facing towards the target. In terms of this article, think of the A1 Rifle style as a “fit” rather than a specific stock. You can get aftermarket A1 rifle stocks in different shapes from companies like Magpul to fit the original size A1 rifle buffer tube.

A2 Rifle

Later, the A2 configuration came about. It had a longer length of pull that facilitated shooting from a bladed stance or prone positions. The combat stance mentioned for the A1 and bladed stance for the A2 are just guidelines. The basic difference is that they are different lengths for different sized shooters and/or use from different positions. If you’re using an A2 rifle stock, then you add an extension to the A1 buffer tube to make it work.

Mil-Spec Carbine

The mil-spec carbine tube is used to mount M4-style butt stocks. It differs from the commercial carbine buffer tube in that it has an outside diameter of 1.14 inches. When looking at parts from different manufacturers, you might see this diameter listed a bit differently, like 1.146 inches, but it’s the same. As long as your stock and tube are listed as mil-spec with a size of 1.14-something you should be good to go.

Commercial Carbine

The commercial carbine buffer tube outside diameter (and butt stock interior diameter) measure 1.17 inches. That’s Because we have to make things difficult and have two different and incompatible sizes. Again, you might see another digit after the 1.17, but that’s OK. Just make sure stock and mounting kit parts are both 1.17-something commercial versions.

The simple takeaway from all this is that there are two lengths of buffer tubes relevant to stock selection: rifle and carbine. If you go with a carbine system, there are two diameters of buffer tubes and stocks: mil-spec and commercial. Make sense sorta?

What Do You Want To Do?

Now that you’ve matched the “physical” dimensions of mounting kit and stock, you can move on to more interesting (and fun) decisions. One of the great things about the AR-rifle platform is that there are billions (well, maybe thousands) of aftermarket parts from which to choose. The industry has gotten very creative with buttstocks and developed stocks that are optimized for all sorts of uses.

What do I mean by uses? We’re all probably familiar with the traditional collapsible M4-type stock. That allows the length of pull, and overall rifle length, to be instantly adjusted. You can change the “size” of the AR rifle to fit most any shooter. Also, the adjustable stock helps when we’re wearing heavy clothes. You can shorten the stock a bit so the rifle still fits properly. When you lose the coat, move it back out. Last, but not least, LE and Military folks benefit from the collapsible stock when wearing thick body armor. The stock adjustment can account for that too.

But there are other use scenarios that you may care about. Are you building an accuracy rifle for long range shooting? Maybe you want to go with a fixed stock, or perhaps an adjustable “sniper stock” that allows you to customize the length of pull and comb height with precision. Maybe you want an exceptionally lightweight rifle. You can choose a minimalist stock that weighs next to nothing. If you’re building a rifle for home defense use, you might consider a collapsible stock option so you can shorten it up for indoor use and open it back up when plinking at the range. The potential uses are nearly limitless, and the beauty of customizing your own rifle is that you can optimize things like the buttstock for the way you want to use it.

If you’ll humor me for a brief moment of randomness, you might want to decide whether you care about a rubber or polymer butt plate/pad. While you’ll sometimes see them called “recoil” pads, my reasons for liking them are far more mundane. You see, when you lean a rifle with a smooth plastic butt pad against a wall or something, it wants to slide around and fall down. That gets annoying! Oh yeah, a rubber or polymer pad will also stay in place on your shoulder due to the stickiness. Some people like that, while others don’t. It’s purely a personal preference issue, but something to consider when choosing a butt stock.

Let’s take a look at some examples of various categories of butt stocks. The good news is that there are far too many great options out there to list, so I’ve created a representative summary list below.

Fixed

If you’re building a long range varminter, or maybe you just like the original configuration, you can mount a fixed stock. The receiver component is the same, all you’re changing is the buffer tube and components, so knock yourself out. Here are a couple of examples.

The Original A1 / A2

You can get fixed stocks in the original A1 and A2 style from a variety of manufacturers. Check Rock River Arms, DPMS and Cavalry Manufacturing just to name a few.

Magpul MOE

Magpul offers versions of the MOE fixed stock for A1, A2 and Carbine configurations. It’ll give you additional sling loop and quick attach options over the original along with a rubber buttpad and internal storage compartment.

VLTOR ARM

If you want to break the traditional rules of how a stock “should” look, check out another fixed A1/A2 drop-in replacement option. This one has plenty of sling options and waterproof battery storage compartments that serve double duty as an excellent cheek weld platform.

Magpul PRS Precision Rifle / Sniper Stock

This is a fixed stock, sort of. It’s the AR15 / AR10 version of those nifty adjustable eight ways from Sunday stocks you see on expensive bolt-action sniper rifles. There are two large inset dials that allow precise adjustment of length of pull and cheek weld. I used one of these during a long range shooting class, and it was amazing how often I adjusted the length of pull when switching between prone and supported positions. It also has a covered Picatinny rail segment on the bottom for attachment of a monopod. That’s the area of my only gripe. That cover constantly wants to slide off. If you don’t use a monopod, ditch the cover completely.

Thordsen Customs AR-15 FRS-15 Butt Stock Kit

If you live in a rights-challenged state, you may want to check out this invention. Technically, it eliminates that evil pistol grip that seems to upset so many for no good reason. State laws are changing, so be sure to check with your local situation to see if this is a viable option for you.

Adjustable

Hang on to your shorts, I counted 32 billion options in this category, so invest some shopping time before you buy. Here are a couple of examples of models I like.

VLTOR IMOD Improved Modular Stock

Yes, VLTOR gets another entry on the list, as will Magpul in a second. Both of these companies make some excellent butt stock options. I love a couple of things about the IMOD. First, the waterproof battery compartments (right and left sides) make smooth and wide cheek weld areas. I also really like the rubberized butt pad with the angled toe. That helps it slide into position easily from the top, and the rubber keeps it in place. I have this one on my go-to AR rifle. Similar, but different is the EMOD stock. It looks different, and is a bit longer, but shares many of the same great features.

Daniel Defense Collapsible Butt Stock

Typically you think of the Daniel Defense folks as a full rifle provider. You can also buy components, like their cool new butt stock to apply to your own build. This one makes the list for its cool factor, but also the neat design of the butt pad. You can run without one for a shorter configuration, or add one of two butt pads to adjust the length of pull and tweak the shouldering characteristics. It’s also got rubberized molding in the cheek weld areas.

Magpul MOE Carbine

You can’t go wrong with a simple setup like this one. It’s basic, yet functional. Notice how the adjustment lever is set inside the butt stock frame. This helps prevent inadvertent movement while you’re out and about doing tactical things. It’s also got a rubber butt pad. The best part? You can pick one up for less than $40.

Brownells M4 Stock Assembly

If you want to stay on a tight budget, check out this complete kit from Brownells. It’s not just a basic collapsible stock, but rather a complete kit that includes buffer tube, spring, buffer and mounting hardware. The whole package is about 50 bucks.

Minimalist

If you want to go really light, or are just one of those folks that uses an uncluttered glass desk, try the minimalist approach.

Battle Arms Development SaberTube BDM-LBS Lightweight Stock

Double Star – AR-15/M16 ACE ARFX Skeleton Stock

Another one that I’ll put in the minimalist category is the ARFX from Double Star. As you can see, it’s about as simple as you can get for a butt stock. It’s so minimalist that it uses your existing A2 buffer tube as the top of the stock. There is a foam cover to make the cheek weld a bit softer. While hard to see, it even has three sling attachment points.

A Word on Pistols and the Sig Sauer Arm Brace

Remember at the beginning when we talked about the four types of buffer tubes and stock sizes? Well, if you’re building a pistol, add to the list. A classic AR pistol also needs a buffer tube to make it work, and you’ll find variances there too.

If you’re building an AR-type pistol, you might consider the Sig Sauer AR-15 Arm Brace. If you go this route, and don’t plan to use it as intended, strapped to your firing hand forearm, then be careful and follow the latest ATF news. As of now, and this can change any day, the device is deemed legal when used as designed. The current ATF opinion is that when raised to the shoulder, this configuration magically becomes a Short Barrel Rifle, subject to NFA status and associated tax stamps.

Installation

Guess what? Installation is almost so easy we don’t even need to cover it here. For most carbine stocks, it’s a slip on type procedure. For many rifle-length stocks, you might need to place a screw to fix the stock to the buffer tube, but that’s about it.

Go forth and shop! I suggest Brownells as they have a great selection and fair prices. Better yet, their techs are always on standby to help you pick the right compatible parts for your build. Find something functional enough, and cool enough, for your personal rifle.

Since GunsAmerica is such a helpful community, if you have had good success with a specific buttstock, let us know in the comments. There are simply far too many to cover in this article, and I’m sure other readers would like to hear your experiences.