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Secrets and Tips for Building Your Very Own 300 Blackout

300 Blackout is a true do-it-all round. Thanks to its ability to run supersonic or subsonic, suppressed or unsuppressed, 300 BLK works just as well as a home-defense round as it does a hunting round. But making it perform means building the correct configuration – and to do that, you need to consider all sorts of factors: Barrel length, twist rate, gas system, what load you’ll be shooting, and much more. Stick around and we’ll give you all the secrets and tips for building your very own 300 Blackout.


300 Blackout: Supersonic or Subsonic? Pistol or Carbine?

Depending on your application, you’ll need to determine which rounds you prefer shooting (and why): Supersonic or subsonic? Subsonic rounds work well for hog hunting at night, or for home defense. Subsonic hollow-points will suffer fewer risks or over-penetrating or lack of expansion. Supersonic rounds will provide that extra accuracy and stopping power at greater distances.

Depending on which discipline you elect, you’ll need to invest in the right gas system.


A carbine-length gas system favors supersonic loads and it reduces felt recoil and overall wear-and-tear on your new rifle. Subsonic loads will require a pistol-length gas system to ensure reliable cycling, especially if you’re gunning with a suppressor.


300 Blackout: Which barrel and twist rate are best?

In determining whether you’ll fire super or sub rounds, you’ll figure out which barrel you should opt for. Supersonic loads operate at higher velocities (thanks to that extra powder in the cartridge) and so they will require less barrel length to provide accuracy and stopping power.

Applying that same logic to subsonic loads means you’ll benefit from a longer barrel.


If you’re going for distance, then supersonic loads will perform their best with a 16” barrel; this will provide the most powder burn. Most shooters agree that any barrel beyond this length provides diminishing returns.


Lucky for us, figuring out which barrel length is best for a pistol setup (with subsonic loads and suppression) is simple: The answer is 9”. This is the length 300 BLK was specifically designed to operate at with a suppressor.


Simple logic also says that heavier subsonic rounds favor a faster twist rate of 1:8 while faster, lighter hunting rounds will work best with a 1:10 twist rate.


Final Configuration: Rifle, SBR, or Pistol?

300 Blackout was originally intended to provide the military’s special operators with a shorter, smaller, and lighter platform that still packs a punch. 300 Blackout certainly fits that bill by allowing shooters to decide whether they want a big ole’ rifle with reach, or a smaller pistol for up-close-and-personal engagement.


If you want to hit targets at medium distances, then a 16” rifle configuration with a carbine gas system (available here) is the formula to crunch. If you prefer a maneuverable pistol meant explicitly for close quarters, then a 7.5” configuration (like our Pistol Build Kit) with a simple brace and pistol gas system is the ticket.


And lastly, If you want the best of both worlds, we recommend finding that sweet spot with a 10.5” barrel and pistol gas system.

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 300-blackoutupper, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.


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