SIG Sauer Announces Supersonic .300 Blackout Ammunition

SIG Sauer has announced a new addition to its nascent ammunition line: Supersonic .300 Blackout. Loaded with 125gr Sierra MatchKing projectiles, this load rounds out the SIG-branded .300 Blackout for their MCX rifle. From the press release:

Newington, NH – SIG SAUER, Inc., designer and manufacturer of the world’s most reliable firearms, accessories, and ammunition, is pleased to announce its new 300 Blackout Supersonic Elite Performance Ammunition Match Grade Centerfire Cartridges. This supersonic round features a 125gr Sierra Matchking projectile and, like the SIG SAUER 220gr subsonic 300 Blackout round, is designed to bring out the best in today’s high-performance AR rifles.

The Sierra Matchking projectiles in the 300 Blackout supersonic rounds are renowned for their superior accuracy, flat trajectory and consistent point of impact. The unique hybrid hollow point bullet design also ensures maximum expansion on point of impact. These cartridges feature match grade brass cases and function with standard 223Remington/5.56mm magazines without a reduction in capacity.

“The 300 Blackout is an increasingly popular caliber with target shooters and 3-gun competition shooters, and is also an excellent round for home defense in short barrel rifles, including the SIG MCX and M400,” said Bud Fini, vice president of marketing for SIG SAUER. “Elite military units are also evaluating the 300 Blackout as their primary CQB load. More modern sporting rifle hunters are turning to the 300 Blackout for close-range hunting of mid-sized game, including hogs and deer. We are pleased to now offer our customers both supersonic and subsonic rounds to meet their shooting and hunting needs.”

All Elite Performance Ammunition is manufactured in the United States by SIG SAUER to the same exacting standards as the company’s premium pistols and rifles. For more information, visit

.300 Blackout in its supersonic form is ballistically very similar to the old 7.92×33 Kurz round, both in energy and trajectory. The primary ballistic difference lies in the very long ogive, necessitated for proper feeding from AR-15 magazines originally designed for longer-cased 5.56mm ammunition.

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


  • ValleyForge77

    I SO can’t wait to get my hands on an MCX pistol/SBR – and excited to see Sig get into the 300 blk ammo game too. I would LOVE to see a review on MCX (9″) soon too. They are already shipping from Cabela’s. Right now, the top 300 blk supersonic round is the Barnes TacTX, IMO – and they will be hard to beat. I’m hoping this helps bring the price down on 300 blk and bring a whole new group of folks into the 300 blk game, lowering prices even further. Bring on the MCX! I’ll deal with the lousy trigger. I always upgrade my triggers anyway. I want to see if it’s reliable, get an idea of accuracy, plays nice with P-Mags, etc, etc. I think I might end up an early adopter, but was hoping to at least get a couple reviews from the big boys first. Fingers crossed.

    • KestrelBike

      I’m considering my first 300blk rifle right now, and already have a silencerco omega on order (my first suppressor!)

      • ValleyForge77

        IMO, 300 Blk is best enjoyed out of a 9″ – especially if you want to run a can on it (that you already have). It’s nothing short of awesome, even without a can and running Supers. My AAC MPW 9″ literally shoots clover leaf patterns and (somehow, surprisingly) has less recoil than 5.56 through a 16″. I can barely wipe the smile off my face when I take it to the range. Only drawback is the expensive ammo, which I’m hoping will continue to come down in price/increase in availability (so seeing Sig release 300 Blk ammo is a good sign). I run the MPW 9″ with an AAC 51T Flash Hider with a QD brake shield on it, so literally zero flash and the little blast it generates goes straight down range, making for a quiet, easily controlled, fully enjoyable shooting experience (until you pay for the ammo). But to me, it’s worth it, and especially if you reload. and the MCX has the quick barrel change to 5/56 (with both barrels included), allowing you to quickly switch to 5.56 in times of economic need. Side folder, piston driven, light, modular as all get-out. Man, I need some data on this thing. Hoping to start seeing some reviews come through soon. Curious about felt recoil with the piston system, of course reliability above all considerations, accuracy, ability to play nice with Pmags, etc. This system has a TON of potential. I guess we’ll see how it all plays out…

  • Core

    Years back immet a local enthusiast at the range had a 300 blk suppressed. It was loud even suppressed, I wasn’t impressed. I’ve used 5.56 nato with gemtech suppressors prior to that time with quieter signatures. I’m guessing his suppressor had issues. I would like to see the ballistics charts on this cartridge.

  • greasyjohn

    I thought at least half the point of .300 AAC Blackout was its subsonic speed.

  • buzzman1

    120 grs? starts to make it look like a 7.62×39 doesnt it.