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300 Blackout Upper vs. 308 Upper

300 Blackout is the hottest new intermediate rifle round to grace the AR 15 world – but why should you stick with it versus, say, a 308 upper? Why not just build an AR 10? Unlike the extreme commonality 300 Blackout shares with your average .223 or 5.56 upper, there aren’t many similarities when comparing to an AR 10 upper. First, let’s hit on what’s similar between the two:

What the AR 10 and 300 Blackout have in common

Mechanically speaking, your typical AR 15 in 308 shares the following components with your average 300 Blackout AR 15:

  • Buttstock assembly
  • Trigger and springs
  • Disconnector and springs
  • Hammer and springs
  • Magazine release and springs
  • Bolt catch roll pin
  • Pistol grip
  • Buffer tube
  • Safety lever

And that’s about it. AR 10 and 300 Blackout uppers share no commonalities – no barrels, upper receivers, bolt carrier groups, or the like will be interchangeable. Philosophically speaking, and when comparing each rifle’s application and benefits, there aren’t many commonalities either.

Why You’d Want an AR 10 Upper

Want to shoot about twice the distance of a typical .223 or 5.56 AR 15 from the bench with a relatively popular, common, and inexpensive round? Then you should look at a 308 upper. Want to still hit quite a lot farther than your typical .22-chambered AR (up to 650 meters, actually) and do a helluva lot of other cool things, too? Then 300 Blackout should be your go-to upper instead.

Your average 308 upper doesn’t do much else besides provide additional reach with an intermediate round. You can reliably shoot out to about 800 meters, but you’re sacrificing some convenience and comfort. Your average AR 10 weighs a heck of a lot more than a standard AR 15, including 300 Blackout.

Even the guy writing this, who built a something-thousand-dollar 308 bolt gun, admits he’d build an AR 15 in 300 Blackout before building an AR 10 in 308. Let’s see why:

300 Blackout is Convenient

Already own an AR 15 chambered in .223 and 5.56? Then you already own a 300 Blackout AR. Don’t believe us? Read our breakdown comparing the two. All you need to do is switch out your barrel and chamber (which can be done with a Dolos QD Barrel System) and you can go from shooting .22 to 300 Blackout. It’s stupidly convenient.

300 Blackout is Accurate

Official ballistic data says 300 Blackout’s max effective range is somewhere just shy of 500 meters, but with the right stuff (like Barnes 110 grainers), you can easily punch targets at 650 meters. We wager that 150 additional meters you get with a 308 upper just ain’t worth foregoing all the other reason why you’d want a 300 Blackout upper instead.

300 Blackout Shoots 4 ways Without Modification

300 Blackout’s true beauty rests in its loads and the common AR 15 configuration: With a carbine gas system, an H2 buffer, and a 1:7 or 1:8 twist in a 10.5” or longer barrel, 300 Blackout will reliably and accurately shoot subsonic, supersonic, suppressed and unsuppressed, or any combination of the two. No other rifle round and platform are capable of managing this, including a 308 upper.

300 Blackout is Perfect for Rifles and Pistols Alike

308 simply pushes too much energy, velocity, and recoil to make for a good SBR or pistol – 300 Blackout doesn’t suffer this same fate. With either load, one can enjoy shooting this dual-purpose round in any size AR 15, and many veteran shooters say they can achieve 1” shot groups at 100 yards using sub-10” barrels. Try that with 308, see what happens.

300 Blackout is Quiet and Comfortable

If you’ve never fired a subsonic gun with a suppressor, you’re missing out on the most enjoyable, quiet, and forgiving range day you’ll ever experience. It’s a little unnerving how quiet subsonic 300 Blackout becomes when suppressed. You can shoot this whisper round without ear muffs and the only thing you’ll hear is the sound of the bolt cycling. Again, try that with 308 (really, don’t).

300 Blackout is a Great Home Defense Round

Any rifle round will over-penetrate and generally, any rifle that shoots a .30 caliber cartridge is just too big and powerful for home-defense. That ain’t the case with 300 Blackout. No, this versatile round keeps adding value. With subsonic loads and JHP bullets, 300 Blackout packs a serious punch – more than any sub gun, and more than most handguns – making it perfect for home-defense. What’s more, an AR pistol or SBR will afford much more accuracy and stability in a home-defense situation when compared to a handgun or big rifle.

We Could Keep Going…

But we won’t. We’ve covered the biggest things: Suppression, pistols and rifles, convenience, range, home-defense, and the like. 300 Blackout is just wonderfully convenient in so many ways, much more so than 308. If every little inch counts, then sure, a 308 upper will be the better choice for smacking steel just shy of 1,000 meters. Beyond that, it’s no competition.


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