How to Choose the Right AR-15 Rifle Stock

In many ways, the AR-15 is the Lego of firearms. Due to its modular nature and the seemingly limitless array of aftermarket parts available, millions of possible gun configurations exist. 

This is also true for the number of AR-15 buttstocks available on the platform. There’s no shortage of options, from fixed to collapsible to PDW-style telescopic and even folding stocks. So, how do you pick the right one for you? Let’s narrow down the selection based on your needs and find out.

Four characteristics should be considered when deciding on an AR-15 stock to determine its worth. The first is compatibility.

Since the AR-15’s recoil spring assembly is located inside the buttstock in traditional configuration rifles and carbines, the internal space inside the receiver extension and buffer weight determines what types of gas systems it can function most reliably with.

Note that this is only the case with traditional direct impingement systems. If you’re running a piston AR or anything other than direct impingement that uses an AR stock, you can use whatever you like - provided it fits. 

The different types of gas systems are based on the distance between the gas port at the front of the gun (This can be either integral to the front sight assembly or a standalone item.) and the gas key attached to the BCG or bolt carrier group. 

• Rifle-Length: 12 inches - 18-inch barrels or longer
• Mid-Length: 9 inches - 14.5-inch to 20-inch barrels
• Carbine-Length: 7 inches - 10.5-inch to 16-inch barrel
• Pistol-Length: 4 inches - Anything under 10.5 inches

The longer the gas port distance, the softer the recoil impulse is because the pressure has time and space to spread out over a distance. This is also true for barrel lengths, so matching them up is essential. With the wrong combination, the gun will either be unreliable or have dramatically increased recoil and mechanical wear.

The same is true for buffer weights and lengths. While most 5.56mm AR-15s today can function regardless of the combination of the gas system, barrel length, and buffer weight, it’s only because they tend to be over-gassed. Several companies do this to ensure that shooters who run poor-quality ammo or who neglect to clean their weapons regularly still have functional guns. 

There are exceptions when it comes to different caliber ARs, especially pistol-caliber ones, which almost exclusively use blowback operation. But I could write a book on buffer weights, lengths, and optimal combinations. Instead, follow this guideline:

• Fixed-stock rifles use a buffer tube that only fits fixed stocks.
• Carbines and pistols utilize shorter carbine-length buffer tubes, and PDWs typically use a proprietary design.

One last thing about stock compatibility. Although virtually all new-production AR-15s on the market use military-spec buffer tubes, older guns are sometimes equipped with commercial-spec tubes. These two types aren’t compatible, so make sure you carefully read the description of the stock you’re looking to purchase. Also, don’t worry if you’re buying a gun from Palmetto State Armory. All PSA AR-15s use military-spec buffer tubes.

A rifle’s stock is the most critical component of any gun’s ergonomics. If the stock is too long, the gun will feel awkward and nose-heavy, making shooting accurately tricky. If it’s too short, it makes using magnified optics difficult because you’ll be too close to the optic to be within the proper range of its eye relief. It also makes recoil management difficult because your shooting arm will be compressed and unable to get good leverage on the pistol grip.

A great example of being too long is for shooters under six feet tall to square off with an M16A2 or A4 clone and see how much they need to crane their neck to get a good sight picture. Ideally, the rifle should be comfortable to aim when the shooter has the gun shouldered while standing upright with their head but still applying pressure to the stock - AKA a cheek weld. 

But these ergonomic woes are precisely why telescopic stocks are so popular. Regarding ergonomics, the only thing better than a stock you can adjust to fit your needs is one that has been custom-made for you.

However, not all adjustable stocks are created equally. Most allow the shooter to position the stock in one of four positions. However, more advanced options will enable the shooter to adjust the comb height (how high your head sits on the stock) and recoil pad thickness; some can even shift the buttpad up or down to fit more precisely inside the shooter’s shoulder pocket.

Generally, if you’re going for an adjustable stock, ensure it has at least four different length positions. Also, I would recommend one that has extra space on top to place your face when shooting. A narrow stock works okay, but a wide, comfortable one means you can put more force on it without discomfort. A great example of this is the B5 Systems Enhanced SOPMOD stock.

This brings me to another aspect of stock ergonomics—sling placement. Original M4 stocks feature two sling mounting options: a metal loop at the bottom and a slot in the middle of the rear. These work great for USGI slings if you’re looking for a way to carry your rifle while walking, but what if you want to transition to a shooting position quickly? For that, you’ll want to mount the rear of the sling closer to the receiver.

One common option is the Magpul ASAP mount. This replaces the buttstock tube mount collar that attaches to the back of the receiver and retains the takedown spring and plunger. This allows shooters to mount the sling closer to the receiver and more easily swing the gun into action. 

Another solid option is a QD mount. Many AR-15 slings now come with a QD mount that simplifies attaching a sling to a gun. B5 Systems stocks and several others now have ambidextrous QD mounts on the side of the stock. This is a great option for shooters who want to mount a sling quickly.

In the world of firearms, many people assume lighter is always better. Which is fair - ask any 0331 Marine if the M249 SAW is fun to carry for long durations. But extra weight does have advantages, especially when it comes to longer-barrelled guns. 

For instance, old-school DCM shooters running bull-barreled M16A2 clones used to install lead wedges into the cleaning compartment of their gun inside the stock. They did this to shift the balance of the gun back toward the shooter, making it less fatiguing to aim and shoulder from the standing and kneeling positions. 

While I don’t suggest adding that much weight to your stock, a solid stock that helps counter the weight of a full-length carbine can make a gun feel much lighter. Alternatively, a lighter stock will be fine if you’re running a 7.5-inch barrel SBR.

Use some common sense and pick a stock that balances well against your barrel’s length and thus, weight.

Under normal conditions, an AR-15 stock sees very little hard use. But that doesn’t mean you should pick the cheapest Chinese-made clone and slap it on your high-dollar rifle. The stock’s ruggedness must be considered regardless of what the gun will be used for—hunting, three-gun competition, long-range shooting matches, home defense, or simply plinking.

For example, a mil-spec M4 stock is very simple and durable; It has very few moving components and is designed to take hard use from soldiers in combat who historically treat the equipment as if it were rented. While precision shooting stocks like Magpul’s PRS Gen 3 are generally rigged, aspects of the stock are susceptible to damage because they feature mechanical aspects like height-adjustable combs and buttpads.

A stock’s mechanical complexity doesn’t always predicate its fragility. Companies like Maxim Defense manufacture a complex PDW-style stock for the AR-15, which is very robust due to its use of aluminum and steel components. Thus, the best way to determine if a stock is rugged enough for hard use is to either determine what it is made from or see if any special military, police, or counter-terrorism units utilize it. 

Think of it this way: if the SAS or the Army Rangers use a particular stock, it has already been vetted in the field under the worst conditions. That doesn’t mean it’s the most cost-effective solution, feature-rich, or ergonomic option, but you’ll at least know you’re not going to break it with hard use. 

While it depends on your budget and needs, ultimately, you want to find a stock compatible with your firearm and most comfortable for you. If that means you’re buying a standard M4 adjustable stock, there’s no shame in that. Bolting on the most expensive stock to your host rifle to make it look cool is fun but ultimately a waste of money. I prefer stocks with positive, tactile controls that are as small as possible and rugged because I treat my equipment like it owes me money, and I’m only five feet, nine inches tall. You will want something more significant if you’re like my 6’4” dad.

Again, it depends, and I encourage you to go to a brick-and-mortar store and try a few out before you buy. If that’s impossible, buy a basic, inexpensive M4 stock and take it to the range a few times. Try shooting from the prone position with a sling attached and adjusting the stock to different lengths. After a few trips, you’ll learn first-hand what does and doesn’t work for you.