Guide for Choosing Buffers, Buffer Tubes, and Buffer Springs

NBS Mil-Spec Carbine Buffer / Receiver Extension Kit - MSRP - $34.95
NBS Mil-Spec Carbine Buffer / Receiver Extension Kit – MSRP – $34.95

The right buffers and buffer springs are necessary to keep your AR-15 functioning properly. The buffer itself serves as an additional weight to aid in the cyclic action of the AR-15, and it also serves as a cushion between the buffer spring and the bolt carrier group.

Buffers Briefly Explained

As soon as the round is fired, gas from the bullet pushes the BCG rearwards. As the BCG travels back, the tail end of the BCG will make contact with the front of the buffer, or the large flat portion you see on every buffer.

When the BCG hits the buffer, pushing it back, it compresses the buffer spring. Once the buffer spring is compressed and the buffer travels back far enough, the spring expands pushing the buffer and bolt carrier group forward.

As the buffer moves forward it advances the BCG ahead into the receiver, stripping another round from the magazine, and stopping at the end of the buffer tube.

What to Consider When Purchasing

You may be in the market for a buffer kit as a means of improving your rifle’s functionality, or simply because these parts tend to need to be replaced over time. Adjusting the types of springs and buffers you use is also one way to optimize gas delivery and reliability. Here are some things to consider when choosing a buffer kit:

Buffer weight

Using the proper buffer weight will keep your rifle operating smoothly and will extend the overall life of the parts. You can also minimize the recoil impulse by adjusting buffer weight.

What buffer weight should you use for your AR-15? The answer to this question depends on many factors, including: the size of your gas port, the length of your gas system, what ammunition you will use, and whether or not you will use a suppressor.

Take a look at the variations in weight below. The weights provided are estimates, since the exact ounce count varies from manufacturer to manufacturer:

3 oz. (the most common weight) Usually uses three steel weights. 

NBS Mil-Spec Carbine Buffer / Receiver Extension Kit - MSRP - $34.95
The best selling NBS Mil-Spec Carbine Buffer / Receiver Extension Kit includes a carbine recoil buffer, plus a carbine buffer spring, castle nut/receiver nut, and a mil-spec receiver end plate –  MSRP – $34.95
Aero Precision AR-15/M4 Carbine Receiver Extension / Buffer Kit - MSRP - $39.95
Aero Precision also offers an excellent American-made carbine buffer in their AR-15/M4 Carbine Receiver Extension / Buffer Kit  – MSRP – $39.95

Heavy or H1:
Consists of one tungsten and two steel weights. Weighs around 3.8 oz.

Typically composed of two tungsten and one steel weight and weighs about 4.6 oz.

Aero Precision’s AR-15/M4 Carbine Buffer Kit contains an H2 buffer weighing 4.6 oz., designed to increase reliability in rifles, carbines or pistols with short gas systems.
Aero Precision’s AR-15/M4 Carbine Buffer Kit contains an H2 buffer weighing 4.6 oz., designed to increase reliability in rifles, carbines or pistols with short gas systems.

Normally uses three tungsten weights to weigh around 5.6 oz.

KAK Industry H3 Carbine Buffer - MSRP - $35.00
KAK Industry H3 Carbine Buffer – MSRP – $35.00
NBS AR-15 .223/5.56 A2 Style Mil-Spec Buffer / Receiver Extension Kit - MSRP - $39.95
Even though the H3 can be used in a carbine set up with proper configuring, we recommend the NBS AR-15 .223/5.56 A2 Style Mil-Spec Buffer / Receiver Extension Kit, which includes a buffer weighing 5.4 oz., plus a rifle length receiver extension / buffer tube and 12 3/4″ mil-spec buffer spring.

Rifle buffer:
Weighs around 5.0 oz and uses five steel weights and a steel spacer.

You can use different combinations of the included parts to tune your buffer weight to your needs.

KAK AR-15 Configurable Buffer Kit - MSRP - $65.00
The KAK AR-15 Configurable Buffer Kit will let you accomplish exactly that! It can be used for finicky builds, 9MM, and special subsonic work, among others.

Buffer Length

The two main sizes of buffers are rifle length and carbine length. It’s important to note that the two are absolutely NOT interchangeable. In general, rifle length buffers are used for standard A2 buffer tubes installed for fixed stock ARs. They are made longer than carbine length buffers so that they can successfully fill the extra space in an A2 rifle buffer tube.

Carbine length buffers, on the other hand, are the ideal choice for most collapsible stocks with carbine buffer tubes. A great deal of stocks available on today’s market use Mil-Spec carbine buffer tubes, however some utilize the commercial spec carbine buffer tubes.

Buffer Springs

Buffer springs may look similar, but they do have differences that can affect your rifle’s functionality. While most rifle and carbine springs have exactly the same diameter, they come in different lengths. A standard carbine spring will measure about 10.5” and have 37 to 39 coils, but a standard rifle spring has a typical length of 12.75 and boasts 41 to 42 coils.

Sometimes, a “twang” sound can occur when firing, due to the fact that most buffer springs rub against the internal surface of the buffer tube. You can reduce this noise by choosing a spring with a smoother surface or a special finish to increase lubricity.

Geissele Super 42 Braided Wire Buffer Spring and Buffer Combo - MSRP - $47.00
Geissele Super 42 Braided Wire Buffer Spring and Buffer Combo – MSRP – $47.00

The Geissele Super 42 Braided Wire Buffer Spring is one of our favorite picks for that very reason. Its unique spring design uses three independent strands of wire, just like the German MG42 Machine Gun.

This concept acts as a harmonic damper and energy absorber by allowing the springs to flex separately from each other, decreasing the chance of spring failure. In addition, this design prevents the spring from losing length and force over a given round count and removes annoying spring reverberations (twang).


All in all, the choice of buffer springs and what buffer weight you want to use is up to you and should be dictated by your needs. Whether you are constructing a competition carbine platform, creating a long range AR rifle, producing a firearm specifically for suppressed use, or building a firearm in pistol configuration for CQB applications, the buffer weights and springs are available to make each one run like a champ during your next visit to the range.   

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3 years ago

I have and AR in which the recoil seems excessive. I’ve fired other AR’s with very mild recoil, I’m trying to learn how to adjust/reduce the felt recoil. I suspect its a combination of springs and buffers, I just don’t know which combination.

Stephen DeLay
3 years ago

Just reviewing Buffer Tube lengths and Buffer Weights. Good information on this site. You offer competitive pricing on your kits as well. Glad I found this site.

Last edited 3 years ago by Stephen DeLay
2 years ago

My 12.5” barrel arm was dumping spent cases around 3:00, I changed the BCG to a Sharpes Rifle xtreme with the DLC FINISH and Iam throwing spent cases at 12:00!
I installed a Red Sprinco and an H2 buffer and now Iam at 1:30-2:00. no FAILURES OF ANY KIND, but Iam not at 3:00 any longer

Ben Dover
Reply to  Blacjac
2 years ago

You’re overgassed. Needs a h3.

2 years ago

I found that the 350 legend with 180 grain bullet cycled much better with the A2 mill spec buffer and stock. Mostly because of the 5.4 oz. buffer.

1 year ago

I have an AR9 build that fails to lock the slide open with an empty mag. I am wondering if the KAK configurable buffer kit would be a good start in my attempt to cure this problem. Maybe that kit along with a stiffer spring? Any help appreciated.

1 year ago

The AR build chamber in 9mm is not cycling correctly. Not sure if I have the right buffer and spring.

1 year ago

Building a 350 Legend and trying to do homework on the proper spring and buffer tube weights for both a carbine and rifle. 18” stainless barrel. There must be a table with these values for each caliber and configuration? Why can’t I find it? No need for purchasing the wrong parts! Any help would be appreciated.

10 months ago

The mil spec receiver extension (buffer tube) requires it to be forged and not extruded aluminum..Any semi auto in 5.56 should run with the carbine weight buffer.The H buffer was used to prevent bolt bounce on full auto with the M-4 and the H2 buffer to prevent bolt bounce on full auto with the M-4A1 which uses a heavier barrel..

Regular Guy
8 months ago

Great article. Very helpful. Thanks bro. Love the website.

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