Be advised of SIG MCX 300 Blackout twist rate and baffle strikes

I got a call from my friends at Stillwood ammunition a few days ago after they were informed by a customer they had experienced multiple destructive baffle strikes from ammunition they loaded using lead free 125gr slotted copper Precision Component Technology bullet. The customer was shooting a new SIG Sauer MCX pistol in 300 Blackout. Josh, from Stillwood, and I brainstormed on what the cause could be, as I have shot literally hundreds of rounds of that ammunition through several platforms and several silencers without any issue. After going through everything I could think of I asked Josh what the twist rate was in that MCX pistol. He told me his customer informed him the twist rate was one in six, and I was sure that was wrong. Josh agreed that seemed awful fast so I took to the SIG website and could not initially find that information. So I searched for the Owner’s Manual for the pistol to find answers and sure enough it states that every model of the MCX has one in six twist rate.

In my opinion, and the opinion of Stillwood and Barnes Precision Machine this is an entirely way too fast twist rate for supersonic 300 Blackout. I called tech support at a well know ammunition manufacturer that I have a relationship with and learned that with such as twist rate the bullet is turning 300,000 rpm. I was also told that even with the .22 varmint bullets designed for a fast one in seven twist at extreme velocities, such as the .220 Swift develops,  the bullets will come apart before you reach 290,000 rpm. So we know 290,000 is beyond redline for varmint bullets designed for fast twist rate and velocities. He proceeds to tell me with that fast twist rate in a 300 Blackout the lightest bullet that could be shot would be 220gr at only subsonic velocities. This information should be easier to locate.

So, it appears that light supersonic bullets can and will come apart due to centrifugal forces from twist rates of one and six in the SIG MCX 300 Blackout barrel and could cause damage to silencers. You need to exercise extreme caution when doing such. Stillwood will be adding such a disclosure to their website. With all that in mind, a one in six twist rated would be optimum for 300 Blackout 220gr or heavier subsonic ammunition.

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10 Responses to Be advised of SIG MCX 300 Blackout twist rate and baffle strikes

  1. David Porter April 16, 2017 at 2:42 pm #

    The twist rate of the SIG MCX pistol in 300 AAC blackout is actually 1:5. Even more extreme RPM…

    • Hunter Elliott April 16, 2017 at 3:43 pm #

      I have had two people tell me the pistol is 1 in 5 but the SIG manual says 1 in 6.
      After talking to a guy that had some supers come apart in a can he confirmed it is a 1 in 5, so you are correct sir.

  2. SK October 21, 2017 at 3:59 pm #

    I have a MCX 9-1/2″ .300BO barrel which is clearly marked “300BO 1/5”.

  3. mh November 8, 2017 at 8:13 am #

    What was the suppressor? If the baffles aren’t right they will destabilize the round. Particularly with subs.

  4. Jan Vornholt March 14, 2018 at 10:50 am #

    Anyone shooting the Hornady 110gr full boar ammo or the Barnes 110 300 blackout ammo in these 1:5 twist rate barrels suppressed ?

  5. Ron Cattera April 2, 2018 at 10:12 pm #

    Why would you want to???? Just run subsonic if your using a can. I have ran Hornady 110 out of 5.5 inch Rattler and it is loud regardless. Thru a TBA Ultra 9. It makes no sense to run supers thru a can. Just saying!!! I did it just to show some people it can be done even with the short barrel. Stupid is what stupid does. I am known for that!

    • Hunter Elliott April 2, 2018 at 11:47 pm #

      Do you honestly not understand why you run supersonic ammunition through a silencer? Many times the rifle or pistol can still be hearing safe with supersonic ammunition and the right can. Supersonic also generally has much better terminal ballistics and provides a better flight path.

    • Mach2Plus February 9, 2019 at 6:59 pm #

      “It makes no sense to run supers thru a can.” Wow, good Lord, you’re living proof of what stupid is, but unfortunately, you’re too stupid to know it..! I run both supers and subs thru all of my cans all of the time, just like everyone else that I shoot with and for good reason — sound suppression — stupid..! That, and we don’t need bother removing our cans whenever we shoot supers… Seriously Cattera, get a life, quit thinking that you know it all, and above all, quit trying to to tell other people how to run their lives…

  6. JW30845 December 25, 2018 at 7:33 pm #

    The latest Q Honey Badger has been changed from 1:7 to 1:5. Wonder what Qs take on this twist is?

  7. Mach2Plus February 9, 2019 at 7:20 pm #

    Hi Hunter. Good article. FWIW, I have both an MCX Carbine and a MCX Pistol. My MCX Pistol (multi-caliber, of course) has a SIG 300 Blackout Barrel and it is stamped/marked at the muzzle end “1/5” (without quotation marks). On another note, my greatest concern, given the multi-caliber ability of both guns is my placing, or that of a friend using my SIG’s, a 300 Blackout round in one configured for 5.56… That, and mistakenly configuring my MCX Carbine with a short barrel supposed to be used only on my MCX Pistol, thereby making it an SBR… Or putting a telescoping MCX Carbine Stock (I have every variant) on my MCX Pistol by mistake versus the “Stabilizing Brace.” After all, they are only identified at the factory, by serial number as being either a Carbine or Pistol, and I can’t tell the difference between them..! I’m getting a headache now just thinking about it..!
    Best Regards.

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