Which buffer for 300 blackout pistol?

Of all the components going into an AR-15 rifle build, the most overlooked is the AR15 buffer weight.

Why? Because it’s hidden inside the rifle stock or AR pistol brace.

Plus, it’s not as exciting to shop for, buy, and upgrade as a new red dot optic, flash hider, or weapon light.

To top it off, nobody can even see you’ve spent money to make your rifle look cool, and we all know that looking cool for the ‘gram is what really matters.

Tune your rifle to perfection by choosing the correct AR15 buffer weights for your setup. (Photo: Maxim Defense)

By now, you should be familiar with AR-15 gas systems.

Gas pressure is forced up a gas port in the barrel, down a gas tube, and into the gas key in the bolt carrier group, to push the BCG rearwards, extracting and ejecting the spent casing.

If you're building an AR chambered in 300 Blackout, the carbine buffer should be used with subsonic ammo and a pistol-length gas system.

Effects of a Bad Buffer

Go with a buffer that's too light, and you'll suffer from excessive recoil and extra wear-and-tear on your bolt, parts kit, and receiver. Too little weight may cause the bolt to unlock early, as well, resulting in a stuck casing. But throw a buffer in that's too heavy, and you'll run into failures to feed, jams, or short strokes. This guide covers the AR-15's numerous buffer weights and what's best for you, and we even dive into picking the right setup for  building a 300 blackout AR, as well as the .308-chambered rifle. We'll also compare the modern carbine buffer to the original rifle buffer.

The typical AR-15 buffer consists of an aluminum casing which houses the buffer's weights inside. The weights are made from steel or tungsten and are inserted inside the casing, separated by rubber pads. This mitigates the shock of recoil energy imparted on the buffer by the bolt carrier. The head of the buffer is capped by a bumper made of high-impact plastic. The bumper, held by a retaining pin, prevents the casing from taking damage when it bottoms out at the back of the buffer tube. The large base of the buffer directly contacts the back of the bolt carrier group.

Assembled and ready for work, the buffer rests inside the recoil spring, with the spring wrapping around the casing. The buffer and spring rest inside the buffer tube, which is secured to the lower receiver via a castle nut and latch plate. Once fully assembled, the buffer and spring compress as the gas system forces the BCG into the tube. Once fully compressed, the spring and buffer rapidly decompress, forcing the BCG into the upper receiver to chamber another round.

The weights inside the buffer matter most. Buffer weights are typically made from steel or tungsten. Different combinations of weights will produce the correct total weight required for your weapon's setup. Selecting the correct weight largely depends on your AR's gas system, whether you're firing conventional supersonic loads or lower-pressure subsonic loads (with or without a suppressor), and what types of cartridges you use most often.

These are the most common "standard" weights you'll find. Carbine, heavy, and H2 buffers make up the bulk of all buffer used by most AR builders and shooters.

We scoured shooter's reports, forums, videos, and plenty of reference guides to figure out what buffer weight is best, depending on your gas system. Compare below to find the optimal buffer for your setup. It's important to know that gas port diameter can also affect which buffer is optimal for yourself. We listed gas port diameters in our Builder's Guide to AR Gas Systems.

The carbine buffer is best used with a mid-length gas system with a 16" barrel, in a traditional 5.56/.223 rifle setup. It may also be used with a carbine gas system, though felt recoil will be increased. Your AR-15 might feel "over-gassed" and punchy. If you're building an AR chambered in 300 Blackout, the carbine buffer should be used with subsonic ammo and a pistol-length gas system.

We like to call the Heavy, or "H", buffer the diagnostic buffer. It's what many shooters turn to if they're running a carbine buffer and their rifle's over-gassed, felt recoil is excessive, or the bolt unlocks too soon because the buffer's too light. The heavy buffer is also best used with a carbine or mid-length gas system in a standard 5.56/.223 rifle. It may also be used in a subsonic 300 Blackout gun equipped with a pistol gas system.

The H2 buffer is usually the best buffer for a  carbine gas system in a 16" rifle, cycling reliably with the least recoil possible. Most shooters report it works just fine with a mid-length setup, too. If you're building an AR pistol with a pistol-length gas system, you will want to stick with an H2 over an H or carbine buffer, though felt recoil may be high. The H2 buffer may fail to fully cycle in a rifle made to shoot subsonic 300 blackout, even with a pistol gas system equipped.

The H3 buffer largely foregoes use in a standard 16"-barreled AR, and is instead typically used for 9" to 11" AR pistol builds running conventional 5.56 or .223 with a pistol-length gas system. Most shooters agree an H3 buffer is the minimum weight required to ensure your pistol doesn't feel punchy with excess recoil. Lastly, the H3 buffer is also frequently used in lieu of a conventional 9mm buffer for AR9 builds, which rely on blow-back to drive the bolt, as its buffer weight is similar. This produces even greater recoil energy inside the smaller 9mm BCG, requiring greater weight.

Important Note: AR9 bolt carrier groups are physically shorter than the AR-15's BCG. While the AR9 operates using an AR-15 buffer tube and spring, the shorter BCG means it will over-travel past the bolt catch with a typical AR-15-length buffer. Many shooter install spacers (with a total length of 0.76" to 0.875") behind the recoil spring to compensate for this over-travel. You can even stack U.S. quarters in the back of the tube in a pinch.

Just as the H2 buffer is meant to dampen recoil and energy over a carbine buffer in a punchy 5.56 rifle, the HSS buffer is intended to tame the AR9s that still feel over-gassed when using an H3 or by-design 9mm buffer. The HSS buffer uses custom weights (though still usually tungsten) with a stainless steel housing to add even more weight.

The big-boy XH buffer is mostly used in high-energy 9mm AR pistols running +P ammo, or .308- and 6.5 Creedmoor-chambered rifles. At 8.5 ounces it weighs nearly three times that of a standard carbine buffer, making it unreliable in most 5.56 and .223 guns. Some shooters do run an XH buffer in 5.56 and .223 pistols, though this is most often because the pistol in question is using a large-diameter gas port.

The AR-15's original buffer is longer than the modern design (you can see it below in spot #4) and it requires a special buffer tube. This longer tube was only used in the M16 with its old fixed stock, before the smaller M4 Carbine was developed in the 1970s. All new, standard AR-15s use the modern short buffer.

All .308 80% lowers and finished lower receivers share the same buffer tube housing and threads with the AR-15. That means you can use an AR-15 buffer and tube on an LR-308 or AR-10 build, but you'll need the right tube and buffer combo to get the appropriate length of travel for the longer BCG and recoil spring. There are five buffers one can use in a .308 build:

From left to right, the following buffers will work in your .308 receiver and tube:

*ArmaLite's carbine buffer weighs the same as the AR-15's carbine buffer.

The following buffer tubes are available for use with a .308 build:

And finally, these are the rules of compatibility:

Q: What is the optimal buffer weight for an AR-308 or AR-10 build?

A: For .308 rifles using a mid-length gas system and carbine tube (the most common setup), a buffer weight of 3.8 ounces to 5.5 ounces works best.

AR9 Buffers: Overview & Best Practices

It's important to note the AR9's blow-back functionality requires a different bolt carrier group that ditches the carrier key and gas system entirely. This means the AR9 bolt is physically shorter than the AR-15's BCG:

Because of its shorter BCG, and because the AR9 can (and often does) use the same carbine buffer tube as the AR-15, the AR9 requires a physically longer buffer to compensate for the difference in BCG travel, unless a shorter tube or spacers are used instead.

AR9 Buffer FAQs

Q: Can I still use a regular AR-15 buffer (with the appropriate weight) and a carbine tube in my AR9?

A: Yes, but it is not recommended. The longer travel of the AR9 bolt can (and often does) break the bolt catch.

Q: What are symptoms of a poor AR9 buffer and tube setup?

A: The AR9's designed to function with LRBO, or last-round-bolt-open. This means the bolt remains locked to the rear once the magazine is emptied on the last shot. If your buffer and tube setup are incorrect, this will typically fail to occur.

Q: What if I want to use an AR-15 buffer and tube for my AR9 build?

A: This is perfectly acceptable, though you'll want to invest in an appropriate spacer. Again, the optimal spacer length is 0.76" to 0.875".

Q: What is the optimal buffer weight required for the AR9?

A: The AR9 buffer must weigh 5.0 ounces or more, to ensure reliability. A weight of 5.4 ounces is ideal.

In simple terms, you would want just enough buffer weight and spring tension to lock the bolt back on an empty bag. If the buffer weight is too light, you probably won’t get any recoil reduction, whereas if it is too heavy, your bolt might even fail to lock back.

The standard carbine buffer systems on the market are usually optimized for the 5.56mm NATO round, usually based on the specifications of a standard military M4.

If you’ve chosen to buy or build your rifle to chamber a 300 Blackout, not only is your caliber non-standard, your rig is highly customized too. Hence, choosing the right weight or buffer spring is going to take some trial and error.

Your recoil spring must be paired with the right buffer weight for your 300 Blackout rifle. A buffer would usually be made from a combination of steel and tungsten to achieve the necessary weight. Different terms are used to identify different weights.

Carbine weight is identified as the standard 3-ounce buffer used in mil-spec carbines. They work with different varieties of ammunition, which is great for mid-length setups.

The H1 carbine buffer weighs around 3.8 ounces and works best on an over-gassed AR-15.

The H2 carbine buffer weighs around 4.6-4.7 ounces. These buffers are mainly for practical use with the recent rise of AR-15 pistols as they wouldn’t be ideal for mid-length systems.

The H3 carbine buffer weighs around 5-5.4 ounces, which is very often used with the .300 Blackout, but in fact, more suited to the 458 SOCOM round.

1 thing you should know is that rifle-length buffers are completely of a different species, and they have a standard weight of 5 ounces, which are not interchangeable with the carbine systems.

It’s not as simple as matching the right buffer system to your .300 Blackout caliber. Just like other rounds, the .300 Blackout has both sub and supersonic variants in a range of bullet weights and each would work best with different spring tension.

Other factors include the barrel length, gas port size, muzzle device, bolt carrier group weight, etc. Carbine springs usually feature 37 – 39 coils and rifle springs could come with 41 – 43 coils.

Carbine recoil springs must be over 10’ to be serviceable and rifle springs must be over 12’. You will notice that most recoil springs look like a solid and steel round wire.

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As one of the largest firearms retailers in the USA, Brownells has enough market data to know what you need. That is why they have produced many great quality products of their own from mere components to complete firearms, and the Brownells – AR-15 Buffer Retainer Springs is no exception.

Everyone knows that any firearm and/or component with the Brownells name on it would offer you one of the best bang per buck on the market. The Brownells – AR-15 Buffer Retainer Springs is the classically styled springs that you can expect to live up to Brownell’s reputation in providing top-notch products for reasonable prices.

It would be ideal if you could have a few disposable back-up springs around the corner so that whenever you or your friend’s .300 Blackout rifle stops functioning, you always have a plan to remedy it.

In terms of material and construction, these springs are guaranteed to be at least, as good as those of original equipment manufacturer (OEM) springs. If you have a nice arsenal of sporting rifles that aren’t shooting as well as they used to, these springs could bring back life to them.

You are looking for a spare spring for emergency purposes. Available on Brownells for only $2.99 per unit, this is as affordable as a buffer spring can get. Seeing that it’s made and manufactured by Brownells themselves, you can rest assured that you will be getting a solid spring with all the top features with a nice and solid construction.

You want something more. For $2.99, you can’t ask for too much besides great built quality and features. If you are looking for a buffer spring with more advanced technical designs, the Brownells – AR-15 Buffer Retainer Springs wouldn’t be your best option.

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Geissele is a company that’s based in Pennsylvania who has built a formidable reputation for itself in the modern sporting rifle scene.

As the name – Geisselle suggests, it means immediate respect down at the range, and with the Geissele Super 42 Braided Wire Buffer & Spring Combo that’s designed to enhance the function and reliability of your rifle, you will be getting that respect from your peers.

The Geissele Super 42 Braided Wire Buffer & Spring Combo is a braided spring with 3 separate wires just like the classic German MG42 machine gun, which is pretty cool. The reason behind this design is so that it can dampen harmonics and absorb more energy as each wire flexes independently.

From there, it will allow your .300 Blackout rifle to be more reliable by lowering the chances of spring failure and displacing any excess energy as you shoot. The braided design of the Geissele Super 42 Braided Wire Buffer & Spring Combo also has a reduced tendency to lose its length and strength over time, making it extremely durable.

This buffer spring is a carbine-length spring which is usually used with a supersonic .300 Blackout ammo. This is because as a relatively stronger spring, it will require more energy transfer from supersonic rounds unleash its full potential.

This extra spring strength would also provide additional reliability when your .300 Blackout rifle is exposed to bad ammo or when you haven’t clean your gun in a while. Another great feature about this spring is its reduction in the twangy noise you might get from legacy springs.

You are a careless shooter. If you are careless and often expose your 300 Blackout rifle to poor quality, steel cased, or dirty ammo, the Geissele Super 42 Braided Wire Buffer & Spring Combo would be a great option for you due to its added reliability.

You want your gun to be quieter. Because this spring emits less twangy noise than you would find in a regular legacy spring, you will get to enjoy your shooting session more without any noise interferences from your spring,

You use subsonic 300 Blackout rounds. Unfortunately, the Geissele Super 42 Braided Wire Buffer & Spring Combo was designed to pair with supersonic .300 Blackout rounds as it is a relatively stronger spring that requires more energy transfer from the likes of supersonic rounds.

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The manufacturer – Aero Precision, is a company based out of Tacoma, Washington, that is specialized in precision machining for the modern sporting rifle scene. This buffer kit isn’t just a simple spring, but a full buffer kit.

Inside the kit, it includes a 6-position mil-spec 7075-T6 aluminum buffer tube, a buffer spring, a carbine buffer (3 oz.), and a lock nut. One thing you should note is that it doesn’t include a stock.

The Aero Precision AR15 Carbine Buffer Kit is one of the best options to have if you have an older .300 Blackout rifle sitting around that you’d want to give new life into. With this buffer kit, you can rest assured as these components are specifically designed by Aero Precision and tested to work well together.

Weighing around 9.8 ounces, this buffer kit is also a great companion that you could tag along on your shooting sessions as a back up just in case anything happens. Since it is precision-machined by Aero Precision to fit your everyday AR-15 solidly, you won’t have any compatibility issues with this buffer spring kit.

In most scenarios, you would be able to fit the spring into your .300 Blackout rifle without any snugs and lateral movement thanks to Aero Precision’s precision machining technologies. Despite being made in the USA, you can still get it at an affordable price, which makes it a great value for money.

You are shopping on a budget. The Aero Precision AR15 Carbine Buffer Kit isn’t just affordable, it is a full buffer system that you can rely on to bring life to any old .300 Blackout rifle. Since it’s a kit with all the tools you need, you won’t have to worry when your gun breaks down on the range.

You are a rough user. Unfortunately, with all the great products, even they have their own shortcomings. For the Aero Precision AR15 Carbine Buffer Kit, it’s the packaging. Some complained about the poor protection by the packaging to the buffer tube finish which some rough users might unintentionally cause damage to.

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If you didn’t know, Palmetto State Armory (PSA) is a veteran-owned, renowned manufacturer of firearms and firearm components based out of South Carolina. PSA is also one of the largest firearms and firearm component distributors in the USA.

Because of that, PSA has all the data and feedback they need to pinpoint what you need. In this case, it’s the PSA PA10 Carbine Buffer Spring.

The PSA PA10 Carbine Buffer Spring is a classic round wire buffer spring that’s applicable in carbine buffer systems. Although it was designed specifically for the use of PSA’s own PA-10 and PTAC Tac-10 lower receivers, it could be used with almost any carbine-sized buffer system so you won’t have to worry about compatibility issues.

However said, the PSA PA10 Carbine Buffer Spring is still optimized to be used along with .308 caliber AR-10 style platforms. As such, it will still essentially work better with supersonic, rather than subsonic 300 Blackout rounds.

In terms of length, the total length of this buffer spring is 11.5’ long and it comes with 31 coils. Overall, the PSA PA10 Carbine Buffer Spring is still a great, affordable option for AR-10 and AR-15 .300 Blackout rifles.

You have a tighter budget. The PSA PA10 Carbine Buffer Spring is essentially one of the best cost-effective 300 Blackout buffer springs on the market. The fact that it was manufactured by PSA is an indicator that you’ll be getting a top-quality buffer spring.

You shoot with subsonic 300 Blackout rounds. As mentioned above, because it was optimized to use with .308 caliber AR-10 style platforms, it will only unleash its full potential with supersonic 300 Blackout rounds.