It is probable that most people’s home builds are built around 5.56, .223 or around a hybrid like .223 Wylde that can shoot both. The former two cartridges have, for a long time, been a favorite among AR-shooters and tinkerers.
We can’t blame them. Both of these cartridges are light, cheap, readily available, small (making them easy to carry), and produce a flat trajectory and good terminal ballistics, making them suitable for everything from long-range shooting to hunting and defensive applications.
But there is another contender out there, one based around the same cartridge, but which offers .30 caliber performance. It’s .300 Blackout, and here’s what a rifle built with a .300 Blackout 16-inch upper will offer.
The Good
First, let’s start with all the potentially positive reasons you might adopt for building an AR-style rifle with a .300 Blackout 16-inch upper. There are plenty of them and these are the main ones.
1. Enjoy superior stopping power at close ranges
The main advantage the .300 Blackout has over both 5.56x45mm NATO and .223 Remington has to do with stopping power, especially at close ranges.
All you need to know to see that full picture here is to get an impression of what muzzle energy is like.
Fired from a 16-inch barrel, a 125 grain .300 BLK bullet can produce as much as 1,360 ft-lbs of muzzle energy. Average muzzle energy from the same barrel for a 55-grain 5.56 round is close to 1,200 ft-lbs, if not lower.
So you get more than 100 ft-lbs of extra energy at the muzzle basically with no change in the cartridge, just a heavier bullet.
This makes this cartridge better for sporting and defensive applications wherein stopping power matters, at least within 100 yards.
2. Hardly any extra recoil over 5.56/.223
With all that extra muzzle energy, you might be expecting the .300 BLK to produce a serious kick, and it would seem like you’d be right. But, in all honesty, you’d be mostly wrong.
Naturally, the .300 BLK, which fires a much heavier bullet, will produce more felt recoil, at least numerically. Actually, in the area of around 10-20% more felt recoil.
But the truth is, this is so marginal of an increase that most shooters report feeling almost no difference between the two. Both are short cartridges that shoot relatively light bullets.
So, if you can shoot 5.56 all day without fatigue, chances are you can shoot .300 BLK all day and your shoulder won’t mind it, either.
3. You can use some of the same parts (or parts you already have)
Actually, you can use a lot of the same parts. Strictly speaking you can convert a 5.56 rifle into a .300 BLK rifle probably with nothing more than a barrel swap.
Which means if you replace the upper, you can theoretically use the same lower, grips, stock, and other parts, although you might not want to use the same bolt carrier or buffer weight. Heavier is probably better.
Also, since the two cartridges are very similar in size, you can also use your 5.56/.223 AR magazines to shoot .300 BLK.
If you have any questions about compatibility, though, consult with a gunsmith.
4. You can repurpose old cases
If you can’t find a steady supplier of .300 BLK but still want to build a rifle with a .300 Blackout 16 inch upper, remember that you can repurpose old 5.56 or .223 cases by widening and trimming them, then reloading them with .300 BLK bullets. So don’t let that stop you from pursuing your dream .300 BLK build.
5. The rifle will be lighter, shorter, and deliver superior handling in tight spaces
The last main reason to build a rifle with a .300 Blackout 16-inch upper has nothing to do with the cartridge, but with the size of the rifle.
The shorter, carbine-length barrel will be lighter, quicker, and easier to maneuver, especially at close ranges. So if you intend to hunt in dense brush, shoot competitively (think 3-gun competition), or keep a .300 BLK rifle for home defense, the shorter barrel may very well be your friend.
The Not-So-Good
Now that we’ve covered some of the selling points of a rifle built with a .300 Blackout 16-inch upper, in the spirit of fairness and candor, let’s cover some of the drawbacks.
1. Give up the long-range game
Regardless of the load, .300 BLK exhibits a badly drooping trajectory. Lighter bullets are bad enough, subsonic bullets are abysmal. On the flipside, both 5.56 and .223, cousins of the .300 BLK, are excellent long-range cartridges. The .300 Blackout is not.
The long and short of it is, if you want to build a rifle for long-range shooting, stay away from two things: .300 Blackout and short barrels.
2. The short sight radius is not so hot
Shooting a rifle with a short barrel can be a good thing, especially at close ranges where handling and maneuverability command a larger premium than pinpoint accuracy.
Which is a sticking point here. A 16-inch barrel produces a shockingly short sight radius that will make it difficult to shoot the rifle effectively (at least over iron sights) at extended ranges.
So, again, keep the close-factor in mind.
3. It costs a lot more (usually)
You can probably expect to pay about twice as much, on average, per round for .300 BLK as you will for either 5.56 NATO or .223 Rem. That’s just a cost of the cartridge.
Granted, there are things you can do to engineer the cost down, such as reloading or buying in bulk, but in general, it’s just a more expensive round.
With all of this sad, don’t let all (or any) of this turn you off. You can still build a really practical close-range rifle with a .300 Blackout 16-inch upper. You just need to get one.
Starting with a .300 Blackout 16 Inch Upper? Get It Here
Now that you know some of the best reasons to build a rifle with a .300 Blackout 16-inch upper, if you feel validated by some of our observations, it means you might have the right goals in mind for the build.
We also carry the parts you need, from stock to muzzle. Get them here, and if you need help or have questions feel free to get in touch with us at Sales@MCSGearup.com before buying.