Modern Intermediate Calibers 009: The 6x35mm KAC/TSWG

The 6x35mm KAC/TSWG flanked by its parent, the .221 Remington Fireball on the left, and the 5.56x45mm on the right, which it is designed to duplicate from shorter barrel lengths.

The 6x35mm TSWG, also commonly called the 6x35mm KAC, is a round shrouded in mystery. Apparently designed by Knight’s Armament Company for the interagency counterterrorist program cryptically named the “Technical Support Working Group” alongside the PDW with which it is popularly associated, the round was apparently never adopted. However, it is interesting primarily as an example of a round with shorter overall length than the standard 2.2-2.3″ (56-58mm) OAL that has become ubiquitous for modern intermediate rounds. The 6x35mm TSWG was designed solely for the unique KAC PDW, but a more traditional AR-15 type rifle called the SR-635 was also chambered for it. Like the .300 Blackout, the 6x35mm was also designed explicitly for 10″ or shorter barrel lengths; KAC has advertised their PDW as being available with 8″ or 10″ barrels. To properly compare the round with both the .300 Blackout and 5.56mm, we will be looking at estimated velocity figures from both 9″ and 14.5″ barrels, although it should be noted that so far as I know, no weapons chambered for the 6x35mm cartridge actually exist with barrels of either of these lengths:


Although not as good a ballistic performer, the 6x35mm KAC is somewhat lighter than the 5.56mm, at about 10.7 grams per round.

Note: All ballistic calculations are done with JBM’s Trajectory calculator, using the ballistic coefficient appropriate to the projectile being modeled, and assuming an AR-15 as a firing platform. Also, keep in mind that there is no single true velocity for a given round; velocity can vary due to a large number of factors, including ambient temperature and chamber dimensions. Instead, I try to use nominal velocity figures that are representative of the capability of the round in question.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • TheSmellofNapalm

    KAC’s an impressively innovative company. Show me another rifle that can go 20,000 rounds with zero cleaning, minimal lubrication and zero firearm-related malfunctions.

    • CommonSense23

      Show me another company that actually put out a realistic maintenance requirements for a product.

      • TheSmellofNapalm

        Do tell

        • CommonSense23

          When I was in sniper school and qualifying on the M110. The instructors talked about the importance of actually reading the manual for maintenance with KAC. Apparently the early M110s/SR25 had copper fouling issues and KAC stated in the manual that the barrel should have a copper cleaner every 500 rounds to maintain
          zero. Well a certain SOF group early on made a bunch of racket about how their guns were losing zero real quick. Well lo and behold they weren’t following the cleaning schedule. After problem was solved. Apparently somebody realized they knew about the schedule but they had ignored it just due to being so indoctrinated with the militaries and certain manufactures asinine cleaning requirements. So they assumed every 500 rounds was really every 1000 to 1500. Which honestly I can’t blame them.

          • TheSmellofNapalm

            Good stuff, man. Crazy how much people love to bash the M110. Did you ever get behind it in country?

          • CommonSense23

            The M110 suffers from the same issues the M4/M16 suffers from in the military. Lack of proper maintenance. Its the same issue as the M249. Unfortunately the military preferrs to wait until the gun breaks before dealing with it instead of true preventive maintenance.
            And unfortunately not. They pulled it out of our armory and replaced it with the abortion of the MK20. And on deployment never spent time any time behind a long gun due to the way were working.

          • FarmerB

            Ouch – what’s wrong with the Mk20?

          • Joe


          • CommonSense23

            I know NSW is still trying to kill the 20s. But like the rest of the SCAR program they have been told its here to stay.
            Ripping primers and downing the gun hard. Random massive POI shifts. A acceptable POI shift of 6 MOA when taking the suppressor on and off. My personal favorite is the gun randomly going full auto. In FNs defense they are proactive in trying to fix the issues.

  • ostiariusalpha

    Now here we go! The 6mm KAC is a fascinating attempt to update the concepts behind the .30 Carbine, as something more potent than the 4.6x30mm & 5.7x28mm PDW pistol rounds, yet softer shooting on full auto than the standard intermediate cartridges.

    • gunsandrockets

      PDW? I like the .19 Badger myself.

      As for an M4 Carbine, I like the 6mm-222 with an 85 grain bullet.

  • mig1nc

    If you are taking requests, I’d like to see the VZ.52’s 7.62x45mm round. It’s one of the most interesting intermediate cartridges to my mind.

    • I’ve got some, so maybe way down the line. Thing is, it ends up being ballistically almost identical to 7.62×39.

      • mig1nc

        Indeed, many fall close together. I love this one though, just enough more than 7.62 Soviet. But I’ve never seen a ton of info on it.

        Plus, this one was actually fielded by a professional army. For a little while at least.

      • mig1nc

        Ok, two more. Once this series is wrapped up, I would LOVE to see two “what could have been” calibers stacked up against these. .276 Pedersen and .280 British. I mean, for no good reason other than it would be cool to see.

        • .280 British is being written now, since it came up in conversation over in the 5.45 article’s comments section.

          .276 Pedersen will happen, too (in fact, I’ve already taken and edited the photo for it), but not as a part of the “intermediate” series, probably.

          Also, if you really, really like the .280 British, I have a huge multi-thousand-word research project-type paper that I’ve partway finished that will be published as part of my “Light Rifle” series.

          If you’ve read Light Rifle so far and are going “huh? You haven’t posted any Light Rifle in ages!” you are correct; I’ve had a lot on my plate this summer, especially with writing shorter posts like this, and the next installment (on the 7.62 NATO’s history) of that post has proven very difficult to create a narrative for. It’s coming… When it’s done. 🙂

          • mig1nc

            Sweet! I can’t wait to see it.

  • kregano

    Man, I haven’t heard much of anything about this round in ages. In fact, the few times I’ve seen it mentioned in the recent past were in relation to “What if” scenarios, like “what if instead of .30 Carbine, the M1 Carbine was chambered in some other round.”

  • Patrick K Martin

    7.92×40 CETME is the one I want to see, I have an idea and I need info (in ENGLISH, which is hard to find to say the least)


    • mig1nc

      That would be interesting to see.

  • Fox Hunter

    My favorite intermediate cartridge, good enough up to 300 yards, and from short barrels at that. Even better than 300 BLK. Someone should make guns and ammo in this caliber.

  • LilWolfy

    I think the 6×35 PDW is overlooked by many, so glad to see it here. It makes a lot of sense for support personnel, crews, and low signature work, but would require a massive change to the logistics system since it is appropriate for so many Soldiers, Airmen, and Marines.

    If they increased the BC of the projectiles and still fit it in those short COL mags it has, it could probably hit 5.56 retained energy at distance and catch up to it. You can carry so many of those mags, more like an SMG. It packs a lot of firepower in a very compact and lightweight package when looking at soldier’s load. You can easily carry 10 mags in the space that would normally take 6 NATO STANAG 5.56 mags. That’s a big deal in the era of body armor.