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 stock 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?

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