Short answer: there are four AR-15 buffer tube (receiver extension) types: carbine for collapsible stocks, rifle (A2) for fixed A2 stocks, A5 for VLTOR's longer system, and pistol for builds with a brace and no stock. Each takes its own buffer and spring: VLTOR says an A5 tube is not compatible with carbine buffers or springs, and that a carbine tube is too short for an A5 buffer. For a standard collapsible-stock build buy a mil-spec carbine tube.
AR-15 buffer tube types at a glance
| Tube type | Stock | Buffer | Spring | Notes |
|---|---|---|---|---|
| Carbine | Collapsible, mil-spec 1.148 in or commercial 1.168 in | Carbine 3.0 oz up to H3 5.4 oz | Carbine spring | The common choice; see our mil-spec vs commercial guide |
| A5 (VLTOR) | Collapsible mil-spec, 7 positions | VLTOR A5 buffers, 3.8 to 6.83 oz; A5H2 (5.3 oz) is the default | Rifle-length A5 spring | Tube 3/4 in longer than a carbine tube; not for AR-10 |
| Rifle (A2) | Fixed A2-style | Rifle buffer, about 5.2 to 5.4 oz | Rifle spring | Needs a rifle-length extension; used with rifle-length gas |
| Pistol | None: slip-on brace | Check the tube maker | Check the tube maker | VLTOR's pistol A5 tube is 1.18 in across and takes most slip-on braces |
Figures are from VLTOR, our buffer weights and mil-spec vs commercial guides, and Magpul, read October 2026.
Carbine buffer tubes
A carbine tube (also called a receiver extension) threads into the back of the lower, carries a collapsible stock, and takes a carbine buffer and carbine spring. It comes in two diameters: about 1.148 inches (mil-spec) and about 1.168 inches (commercial), and stocks fit one or the other. Most aftermarket stocks are mil-spec.
Rifle (A2) buffer tubes
A rifle-length tube is longer and carries a fixed A2-style stock. It takes the rifle buffer and rifle spring, and Magpul notes that putting its MOE Rifle stock on a carbine means fitting a rifle-length receiver extension plus a rifle buffer and spring. See our fixed vs collapsible stocks guide.
A5 buffer tubes
VLTOR's A5 system is a matched set. Its RE-A5 tube is a 7-position mil-spec extension, 7 15/16 inches long, and VLTOR says it is 3/4 inch longer than a standard carbine tube. The buffer is longer too, to hold an extra tungsten weight, and the spring is rifle-length. VLTOR makes five buffer weights, from 3.8 to 6.83 oz, and its A5H2 (5.3 oz) is the default for 14.5 to 16 inch barrels. The A5 kit contains the RE-A5 tube, an A5H2 buffer, an A5 spring, a lockplate and a castle nut. VLTOR says the A5 is not compatible with the AR-10.
VLTOR also claims the A5 cycles more slowly and smoothly, lowers bolt carrier speed and keeps working across suppressed and unsuppressed setups without gas block adjustments, and cites Marine Corps testing without publishing the data. Those are the maker's claims.
Pistol buffer tubes
A pistol tube has no stock. VLTOR's pistol A5 tube is 1.18 inches across and takes most slip-on arm braces, but not adjustable ones such as the SBA3 or SBA4. Putting a stock on a pistol with a short barrel makes it a short-barreled rifle: see our AR pistol guide.
A5 and carbine buffer tubes, with today's prices
Lowest price across the stores we track:
VLTOR A5 receiver extension tube
Pros
- 7-position mil-spec, 7 15/16 in long
- 3/4 in longer than a carbine tube
Cons
- Needs the A5 buffer and rifle-length spring
A5 tube
VLTOR A5H3 heavy buffer (6.08 oz)
Pros
- A5 buffer with more tungsten
- 6.08 oz
Cons
- Only for A5 tubes
A5 buffer
Sons of Liberty Gun Works mil-spec A5-length 7-position tube
Pros
- A5-length tube, mil-spec
- 7 positions
Cons
- Check which buffer and spring it needs
A5-length
BCM mil-spec 6-position receiver extension
Pros
- Mil-spec carbine tube
- 6 positions
Cons
- Carbine buffer and spring only
Carbine
Battle Arms mil-spec 6-position buffer tube
Pros
- Mil-spec carbine tube
- 6 positions
Cons
- Carbine buffer and spring only
Carbine
Rifle and pistol buffer tubes, with today's prices
Luth-AR A2 buttstock extension tube
Pros
- Rifle-length tube for A2 stocks
Cons
- Needs a rifle buffer and spring
Rifle (A2)
Tacfire AR-15 pistol buffer tube
Pros
- Pistol tube for a slip-on brace
Cons
- Not for a collapsible stock
Pistol
How to choose a buffer tube
- Start with the stock. A collapsible stock needs a carbine tube (mil-spec or commercial); a fixed A2 stock needs a rifle tube.
- Then the gas. Rifle-length gas goes with a rifle buffer system; see our buffer weights guide for carbine buffers.
- Never mix systems. VLTOR's warning: do not run carbine parts in an A5 tube or the reverse.
- Buy the matched set. The A5 kit comes with the tube, buffer, spring, lockplate and castle nut.
Compare every buffer tube by price, and plan the build in the AR-15 builder, which flags a stock that does not match your tube. See also our best stocks guide.
Frequently asked questions
What is an A5 buffer tube?
VLTOR's RE-A5 is a 7-position mil-spec tube, 7 15/16 inches long, 3/4 inch longer than a standard carbine tube, used with a longer A5 buffer and a rifle-length spring.
Can I use a carbine buffer in an A5 tube?
No. VLTOR says the RE-A5 is not compatible with carbine buffers or carbine springs, and that you should not mix and match.
What is a receiver extension?
Another name for the buffer tube: the tube that threads into the back of the lower and holds the buffer and spring. Stocks slide on it.
What is the difference between a rifle and carbine buffer tube?
A rifle tube is longer, carries a fixed A2 stock and takes a rifle buffer and spring; a carbine tube is shorter, carries a collapsible stock and takes a carbine buffer and spring.
Is the VLTOR A5 compatible with the AR-10?
No. VLTOR says the A5 buffer is not compatible with the AR-10 platform.
What buffer tube do I need for an AR pistol?
A pistol tube made for your brace. VLTOR's pistol A5 tube is 1.18 inches across and takes most slip-on braces but not adjustable ones.
