New from Phase 5: The HEX-2 Pistol Buffer Tube

Adding to their extensive pistol buffer tube line, Phase 5 has released the Hex-2 Pistol Buffer Tube specifically for the Sig pistol brace. The Hex-2 builds off the aesthetic base that characterized the HexOne, opting for machined scallops instead of the round tube common to other offerings. The scallops blend fluidly with the lines of the Sig brace.


Phase 5 states they worked with Sig Sauer directly with other feedback from “firearms instructors, law enforcement professionals and AR Pistol enthusiasts alike.” The Hex-2 is machined directly from 7075 T7 billet aluminum and includes an anti-tilt extension for those using piston-driven uppers. The tube is designed to use standard carbine springs and buffers.


The basic Hex-2 package is available directly from Phase 5 for $59.95. It includes the tube, end plate, nut, pistol foam pad, and the billet SB15-AP (accessory plug) brace cap . A complete buffer tube kit with spring and buffer is also available for $79.95.


Nathan S

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

The above post is my opinion and does not reflect the views of any company or organization.


  • braceyourself

    that’s great. You know what we really need though? a tube that is 4-5″ longer for our “pistol brace”. Some of us have long forearms and don’t like to shoot nose to charging handle.

    • I could go with that:-)

    • echelon

      KAK tube with spacers. I use it on my 11.5″ AR with Sig brace and it’s awesome.

      • Raven

        I’d be hesitant to do that. Seems like adding spacers is the kind of thing the ATF could use to fuck you over for constructing an SBR, since you’re modifying the stock to allow shouldering.

        • echelon

          KAK sells them on their website as part of the buffer package and specifically says that it’s to add length when using the SB15.

          Also refer to the ATF letter that is public that specifically states that shouldering the SB15 does not convert the “pistol” to an “SBR”.

          I could link it, but just do a search on this very site. TFB posted it a few months ago, if that.

          • Raven

            I saw the letter and all, but I just get the feeling that modifying it any further may take you into a grey area, which is not where you want to be with the ATF.

          • echelon

            I’m not worried. Besides, the reason to do so is also logical from the “pistol” aspect of it as well.

            If you have the brace up close to the end plate of the “pistol”, depending on the length of your arm, it ends up strapping up fairly close to the wrist which doesn’t aid in shooting one handed, which is what the thing is designed to do.

            By putting spacers on the tube and then strapping the thing around my forearm it is closer back to the elbow and adds much more leverage and comfort when firing one handed.

            If anyone questioned all I would have to do is demonstrate the fact. But again, the ATF ruled that using the brace in a matter that was not intended doesn’t alter the classification of the firearm. The spacers are not altering the brace in any way, they are in fact, enhancing its’ natural use.

        • Cymond

          I don’t see how adding spacers is any more of a grey area than using an extra-long tube. Both are modifications to make it longer. If you can justify one, you can justify the other.

  • SafeArmsReview

    I have the KAK on a pistol conversion kit and it works well. With that said I think the Phase 5 Hex2 will brace the SB15 more than the KAK.

    Good stuff

    • echelon

      Phase 5 should make Hex spacers. I do like the end cap though, that’s pretty cool.

  • Phil Hsueh

    Not to be a negative Nancy about this but what relevance does input from “law enforcement professionals” have on the design of this tube? Do any law enforcement agencies actually issue/use AR pistols with Sig braces, if not then I don’t see any input coming from them having any more value than your average Joe who uses AR pistols with Sig braces.

    • Steve Truffer

      Quality of friction fit- even if you grab the brace to yank the gun out of the back of a squad car, and the grip or Magazine catches on the door, will it still hold?
      That’s the only thing I can think of.

      • gunslinger

        but as said, how many LEOA actually use ARpistols w/brace?

        • Steve Truffer

          I doubt any use it duty-wise. Like I said the “LEO” part is probobly the test I mentioned above.

          • Phil Hsueh

            Most likely the LEO “test” is just some cop who tested the tube on their own personal AR pistol so it’s technically LEO tested, just not in any official duty capacity.

          • Ken Montes

            Steve with all due respect, many LEO are using the Phase 5 Pistol. California, Illinois and more … mostly by K-9 guys and SWAT breachers.

    • David

      The LE angle is just marketing bs

      • gunslinger

        winner winner chicken dinner.

    • Ken Montes

      YES lots of LE use the AR pistol with and with out the sig brace!

  • Cymond

    I’d like to see a side-by-side comparison of the KAK, Phase 5, and Midwest Industries tubes. They all have a raised ring for the Sig brace, but there are probably differences in length. The Phase 5 has a storage plug for the excess length, the Midwest is extra long to fill the gap, and I know the KAK is extra long but idk if it fills the gap completely.
    I’d like to make my selection based on the length that is best for me, without resorting to spacers if possible. I haven’t put together an AR pistol yet due to the difficulties in California, but I’m still really excited about the SB-15 (and I think it’s an even bigger deal than 2011-4).
    Even UTG is making a buffer tube for the SB-15, but they’re not much cheaper than the tubes from KAK or Midwest.

    • Cymond

      Ok, it seems from a video that the KAK tube is also long enough to sit flush with the back of the SB-15, just like the Midwest tube. I’m not sure if they both have the same amount of ‘offset’ from the fully-forward position. (ie they may have a different length of pull).
      I do know that the KAK tube extends 8.45″ past the endplate, but the Phase 5 extends about 9.5 with the SB-15 installed. The Phase 5 costs $18 extra, but includes a nut and standard end plate (not worth it to me). One idea for the Phase 5 would be to add weights to the storage compartment to alter the balance of the gun a little bit. I personally think the Phase 5 tube looks great, but that’s just fashion (which changes), but it’s probably heavier due to the decorative hex shape.

      • Stephen

        One thing that swayed me to the Phase 5 over the KAK is that the Phase 5 is made with 7075-T7 vs 6061 of the KAK.

        • Cymond

          That is a good point, and one I overlooked. My primary concern is getting a tube that is the right length for me. I may not always put my arm in the brace, but I definitely don’t want it to be tooooooo long to use the brace. The KAK tube is just right for my arm. Any longer and the brace would be over my elbow.
          FWIW, these tubes are already a heavier profile/diameter, so I’m less concerned about strength. They still have a standard 1 inch inner diameter, but the outer diameter has been increased from 1.15 inch (milspec) to 1.20 inch.
          I originally wrote that post to help me understand the differences between the tubes, and to help anyone else who stumbled across it.