What are the best buffer tube kits?
A balanced firearm is a beautiful thing. Not only is it easier to shoot and less prone to wear and tear, shooting a truly balanced gun is satisfying in a way less orderly set-ups can’t touch.
In addition to being one of the best ways to dial-in the feel of your rifle, no AR-15 build is complete without a buffer tube kit. These unassuming collections of parts are one of the easiest ways to work out the kinks in your set-up and improve your shooting experience.
Be it building a custom AR or upgrading from bone stock, it’s incredibly important to understand the minor differences in these critical pieces of your rifle. Buffer kits are a must-have, but — just like any other component — it’s important to remember not all parts are made equal.
Palmetto State Armory
Palmetto State Armory while not just buffer kits, PSA has a wide array of complete lower build kits which include buffer tubes, buffers, and components, as well as buttstocks, grips and the lot. They come in a variety of colors as well as pistol options and are an easy way to ensure you’re getting compatible components in one fell swoop.
Aero Precision makes a carbine length AR-15 buffer kit with the option of choosing an H, H2, or H3 buffer. This kit comes complete with a buffer tube, buffer, buffer spring, endplate, and castle nut, and is also available in an enhanced version which includes nice touches like Carrier Support Extensions that prevent carrier tilt and minimize wear.
When paired with their lower parts kit you get a high-quality build that’s designed to play nicely together.
Brownells AR-15 rifle length buffer tube kit is mil-spec and will fit all rifle length buttstocks. It is made from mil-spec 7075 aluminum and features a matte black hardcoat anodized finish, for that true black rifle feel.
Luth-AR sells a mil-spec or commercial carbine length buffer tube kit for the flexibility to accommodate either stock on a rifle build. It comes complete with the buffer tube, lock plate, buffer, and spring. Luth-AR makes some of the best buttstocks available, and these can be purchased as a bundle with the correct buffer assembly. No muss, no fuss.
What is a Buffer Tube Kit?
Here you can see the bolt, buffer, and buffer spring working in concert.
A buffer tube kit contains all the components of the buffer tube assembly; the buffer tube itself, the internal buffer (which sits inside the tube), a buffer spring, an endplate, and a castle nut.
When assembled on an AR, the buffer and action spring assembly are housed within the buffer tube and help complete the firing sequence by returning the bolt and carrier to their fully forward position after being slammed open by the gasses of a fired round.
Buffer & buffer tube length
Buffer tube kits are available in two lengths, both of which are specific to one kind of AR or another. What does this mean? Just like barrels, handguards, and other AR components, before you make a purchase it’s key to determine if you’re working with a rifle-length or carbine-length AR.
Unlike many other AR parts, these two buffers — carbine and rifle — are completely different lengths, so they aren’t interchangeable. Rifle buffers are much longer and designed to be used in standard buffer tubes with fixed stocks.
Carbine buffers are shorter, used in carbine-length buffer tubes, and are designed to accommodate adjustable stocks. These days, 9 times out of 10 you’ll want a carbine buffer.
While it’s possible to piecemeal the components one-by-one, purchasing a kit is the easiest way to ensure you’re getting all the correct components to complete or update your buffer tube (also called the receiver extension tube) and internals.
These simple assemblies help manage recoil, save your gun from wear and tear, and connect the buttstock to the end of your rifle.
One thing to note — if you want a quick detach (QD) option point on the back of your upper receiver, you’ll need to verify that the kit includes a QD-compatible endplate.
Why would you need one?
Buffer tube kits are critical because the weight of the buffer coupled with the tension in the spring absorbs the force of firing a round, which assists in managing recoil and cycling the rifle. Different weights and spring tensions can change the feel and characteristics of a rifle. The buffer tube also physically connects the buttstock to the rifle.
The buffer tube houses the two crucial components – the buffer and the action spring. The spring is decompressed into the buffer tube and the buffer sits inside of the spring, making contact with the bolt when attached to the rifle.
When the rifle is fired, the bolt slides back from the gas expulsion, hitting the buffer, and compressing the spring inside of the buffer tube.
This compression stores energy in the spring which expands once the bolt has traveled rearward enough to allow the spent casing to be ejected. The expansion of the spring is what moves the bolt back into place, chambering the next round.
Mil-spec vs Commercial Buffer Tubes
There are two standard types of buffer tube kits; mil-spec and commercial. Mil-spec buffer tubes are built two-hundredths of an inch smaller than a commercial tube. Why should that matter? Because that slight change in diameter means the two are not interchangable. The buttstock has to match the tube size or it will not assemble correctly.
They’re also made from different material. Mil-spec buffer tubes are forged from 7075 T6 aluminum, which offers higher-strength and more stress-resistance than the 6061 T6 billet aluminum used in commercial buffer tubes. 6061 T6 aluminium is easier to weld but has a lower strength & durability.
It’s also very common to see buffer tubes cerakoted, duracoated, and anodized, so you can find one that fits the bill on your custom build.
Carbine vs Rifle Buttstocks
The stock you choose for your rifle needs to match the buffer tube kit. If you’ve purchased a rifle buttstock, you’ll need to use a rifle buffer tube and vice versa with a carbine buttstock.
In some cases, instead of purchasing a buttstock and buffer tube kit separately, you can purchase the buttstock with its matching buffer assembly, which ensures the two will play nicely together.
Buffer Weights & Classifications
The last thing to note about buffers is that they are classified under three different types of weight categories.
Heavy “H” buffers, generally 3 ounces in weight, are used in many stock rifles to cut down on felt recoil when “over gassed”. A heavier buffer provide more resistance against the bolt, requires more energy than lighter buffers to travel the same distance.
“H2” buffers are heavier than H buffers and can cut down on recoil even more. “H3” buffers are the heaviest of the lot.
Buffer weight is important for balancing recoil, which contributes directly to the life of your rifle internals. If your buffer is too light it won’t absorb enough of the firing energy. This causes the recoil forces to be transferred into the internals as your bolt slams into the rear of the buffer tube, which wears down on your bolt and receiver faster.
The opposite isn’t any better. An overly-heavy buffer can cause a short stroke if too heavy for your set-up by hindering the bolt from traveling fully reaward. This can prevent the chambering of the next round or cause jams and misfeeds.
Similarly, if you have a lightweight bolt carrier group, a heavy buffer can cause feeding and cycling issues when the BCG is not heavy enough to move the buffer and buffer spring fully backwards.
Always try and keep these two components consistent so you don’t run into any issues with your rifle’s function. The components also contribute to the overall weight of your rifle, so factor that in as you build your parts list.
It’s incredibly easy to get lost in the weeds of an AR-15 build. The best way to make sure you stay on track (and actually build what you want) is to start with a list of all of the components you’ll need for your build, with the buffer tube kit and buttstock mapped out together.
Since these two components must be compatible, it’s important to shop for these at the same time using the same criteria.
- Thomas Schwenke, M16 and AR-15 – How firearms work! (Animation), February 23, 2019
- Stag Arms Blog, Commercial vs. Mil-Spec Buttstocks
- Strong Side Tactical, Buffer Tube Variations Explained
- The Metal Press, 6061 vs 7075 Aluminum
- Google Patents, Firearm buffer system and buttstock assembly
- 80% Arms, AR-15 Buffer Weights: What The Difference Is, and How to Choose
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