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300 Blackout Upper vs 223 & 5.56 Uppers

So, with all this craze about 300 Blackout, plenty of questions surround the new (and really, same) AR 15 parts associated with the black rifle’s new whisper round. Let’s break down the similarities between your average 300 Blackout upper and your average .223 or 5.56 upper – we promise you’ll be surprised at just how alike these two uppers are.

Barrel assemblies

Okay, this is perhaps the biggest (and really the only) difference between 300 Blackout uppers and .22-caliber uppers. Obviously, the 300 Blackout is a .30 caliber, and trying to shove one through a .22 caliber barrel would result in some nasty injuries.

Beyond that, though, 300 Blackout upper thrive on the AR 15’s gold standard, 16” barrel length and they even use the same M4 feed ramps. They even share similar twist rates – if you want to reliably and accurately shoot both supersonic and subsonic 300 Blackout (suppressed or unsuppressed) you’ll need a 1:7 or 1:8 twist rate. That just so happens to be the standard twist rate found on most .223 or 5.56 ARs.

Gas Systems

If you’re what most consider a “typical” AR owner, you’re likely rocking that common 16” barrel length on your current AR. And attached to that 16” barrel is probably a carbine-length gas system. Well, look at that! Every 300 Blackout upper you’ll come across features either a pistol- or carbine-length gas system! They even use the same diameter gas block and gas tubes as a .223- or 5.56-chambered AR 15.

There’s good reason for this: Pistol and carbine gas systems provide the perfect balance of recoil energy to reliably cycle the bolt carrier group when firing 300 Blackout in supersonic, subsonic, suppressed, or unsuppressed.

Upper Assemblies

Speaking of bolt carrier groups… Think they’re any different in a 300 Blackout upper? Surely they must be! AR 10s use a bigger bolt carrier group. Think again: 300 Blackout uppers use the same exact bolt carrier groups as .223 or 5.56 AR uppers. Same charging handle, too. Yes, the convenience factor is high, here. Know what that means?

Lower Assemblies

You guessed it: 300 Blackout AR 15s use the – say it with us – same exact lower assemblies as .223 and 5.56 AR 15s! Same trigger assemblies, same springs, same bolt catches, same forward assists, same grips, same dust covers and ejection ports, you name it. All the same. And guess what that means?


Right again! AR 15 are technically interchangeable with 300 Blackout rounds. We say technically because they tend to lose some functionality and reliability when loaded to 30 rounds. But if you keep it below 30 rounds, you can sling 125-grain or 225-grain 300 BLK just as well as any XM193 or M855, out of the same magazines – STANAG, Magpul, whatever.

Buttstock Assemblies

And that brings us to our next topic. We’ll spell it out even though it doesn’t really need to be said at this point: 300 Blackout uppers use the same buffer tubes, springs, and buttstock assemblies as .223 and 5.56 uppers.

The only difference may lie in the buffer itself. In order to cycle both subsonic and supersonic loads, 300 Blackout buffers need to weigh between 3.7 to 4.3 ounces, generally speaking. There are some heavier AR 15 buffers for guys slinging heavy loads, and those buffers might not work too well in a 300 Blackout – but they’re technically all universal.

Convenience is Key

So why does all this matter? Convenience, of course! If you’re already an AR owner (chances are, you are if you’re reading this), then you have such an amazing opportunity to swap your existing rifle over to a 300 Blackout – you literally need not change a thing, except for the barrel.

If you’ve learned anything useful about 300 Blackout by browsing our articles, this should be very exciting.


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