The AR-15 is probably just about the most important rifle you'll ever add to your arsenal, and of course the rounds that go into an AR-15's magazine are of critical importance as well. The rounds you choose for a given application—target practice vs tactical readiness vs hog hunting—will play a huge role in your success rate.
Why Do People Use .300 blackout rounds?
The 300 Blackout is a .30-caliber round originally created for shorter barrel rifles and closer-in shooting, such as in CQB and urban scenarios. The round comes in subsonic (less than 1100f/s) and supersonic varieties.
Easy to Suppress. With a good suppressor, the subsonic can take down an attacker without necessarily alerting his friends in the next room. The downside of a 300 subsonic is that it's a heavier round with less powder and thus is traveling slower. So it may not have quite as much take down power as its supersonic sibling. But its stealth capability and effectiveness in shorter barrels make it ideal for use in close contact situations.
Ideal for Shorter Barrels. Speaking of barrel length, ideally I want to have as short a barrel as I can without sacrificing the performance of a round. If I'm weaving in and out of structures, fighting closer in, this is the round for me, both the subsonic and supersonic versions, because they operate well in shorter barrels.
A Strong Punch Closer In. The supersonic 300 of course is not going to behave as quietly with a suppressor, but the increased velocity added to the heavier 300 round will come in handy when I need that shorter barrel but a bigger boom.
Less Gas in Your Eyes. And with either 300 blackout round—subsonic or supersonic—the gas blowback is less likely to block your view in those close quarters, when compared with the rear gas expenditure of a 5.56.
That Cool Name. Who doesn't want to chamber something called a 300 Blackout?
When to Use the 5.56
The 5.56 is, of course, the standard AR-15 round for good reason. If you're hog hunting or defending a position against an onslaught of zombies a football field away (or maybe significantly closer), you want this kind of pinpoint accuracy and speed so they don't end up on your doorstep. Here's why:
It's faster. At about 3,000 f/s, this round screams out of the barrel.
It's lighter to carry. Whereas the 300 is a heavy .30 caliber round, the 5.56 is a .22 caliber (no it's not the same .22 caliber rim fire long rifle round in your 12-year-old plinker). So you can carry more of them.
It's got a longer range of effectiveness. Because of its speed, this bullet is a bit of a marathoner. Because it's got more powder and is a lighter projectile, it can cover the distance needed with great accuracy (given that you have a quality barrel with enough length—like 16-18 inches for optimal performance).
It's significantly less expensive. Because this is the standard NATO round used by many armed forces around the world, it's supply and demand ratio works in our favor (at least for now). Bidenomics are changing things every day, but anyway.
It can be found in abundance. Let's hope that doesn’t change. And if the apocalypse happens tomorrow, you're more likely to find a bunch of 5.56 rounds to restock your ammo cache.
What If I Can't Decide Between 5.56 and 300 Blackout?
You could just drop the bucks and buy two guns and two (or three) stockpiles of ammo, or you could get your 5.56 rifle and then buy a 300 Blackout upper down the road. Interchanging the uppers is a matter of moving a pin.
You'll probably need both for the zombie apocalypse. Sometimes you've got to be real quiet and just take a zombie out, and you don't want to draw a crowd of flesh eating zombies. Other times, you've just got to go full crazy 5.56 and drop them all. There's a time and place.
Now, if I'm getting mobbed by a bunch of zombies, I think I want my 300 blackout for the heavy rounds at close range. Plus, those 300 blackout supers are perfect for a good hog hunt. Those pigs can get big and I need the heavier round to shred them down.
Conclusion? I'm glad I have a bunch of 5.56 guns and rounds, but I should have more of the 300 Blackouts. But hopefully overall this all has helped you decide what's best for your arsenal.
And whatever round and upper you use, make sure you get good instruction on how to deploy it in a variety of settings.
Train Hard. Train Smart. Live Free.