Let’s not mince words. If you build a short barrel rifle or an ARP with a .300 Blackout AR upper, it is likely going to perform better than one chambered in 5.56.
That is not to suggest that .300 BLK is better across the board. We all know it isn’t. It’s terrible at long ranges.
But no one builds an ARP or SBR for long-range shooting, so we’re back to square one, and if what you’re looking for is performance from a shorter barrel, you’ll get that in a .300 BLK build.
So let’s take a closer look at why that’s the case.
Why a Short Barrel .300 Blackout AR Upper Will Offer Better Performance Than 5.56
There are several things at work here which give a short barrel .300 Blackout AR upper the clear advantage when compared to a 5.56 upper.
One is that the .300 BLK relies mostly on bullet mass to deliver its results. The 5.56 relies mostly on speed.
A longer barrel is necessary to trap the expanding gases for longer in order to deliver for the 5.56. As a result, a short barrel upper, or worse, an ARP upper, will lack the barrel length to deliver sufficient muzzle velocities for the 5.56.
The end result of firing a 5.56 from a short barrel upper is anemic performance. There are worse options, but a cartridge like this just doesn’t offer the promised performance from a shorter barrel.
Another thing about this, which is also tied to velocity, is that a shorter barrel generally allows all the propellant charge behind a .300 BLK bullet to deflagrate before the bullet even leaves the bore.
Therefore, not only do you get solid, intended performance from a shorter barrel .300 Blackout AR upper, by adding barrel length you wouldn’t get any advantage. There’s just no point past a certain length.
The consequence of this is that .300 Blackout performs well from short barrels. Not just short barrel rifles under 16 inches, but from ARP barrels. A 10 inch barrel is really all you need with .300 BLK and it performs well even with shorter barrels.
Reliable cycling with a shorter barrel upper is another thing with .300 BLK. The added mass of the larger, heavier bullet makes the .300 BLK preferable because it results in a generally more reliable build than one chambered in 5.56.
As for accuracy at closer distances, that’s a wash. The 5.56 is inherently more reliable at greater ranges, especially from a longer barrel, but let’s just be honest. No one builds an ARP or even an SBR for tack-driving accuracy at 100 yards or more.
Therefore, at close ranges, accuracy is really a wash. The ranges at which you’d find yourself engaging targets with a .300 BLK or 5.56 ARP or SBR makes this a nonentity.
Another note here is the stability of the heavier bullet at lower speeds. The faster, lighter 5.56 performs better with a longer barrel, greater velocity and a higher rate of twist. These things just aren’t necessary to keep .300 BLK stable at lower velocities.
Why a Short Barrel Upper Is Advantageous
Whether or not you build with a .300 Blackout AR upper or choose another caliber, unless you are building a long-range rifle, there are many reasons that an ARP or an SBR might serve you better. Here are just a few.
- Lighter overall build. With an ARP or SBR, you can make a platform that is a lot lighter than a full-size rifle and which can therefore be carried and fired for longer with less fatigue, recoil aside.
- Better handling in tight quarters. The shorter barrel length of an SBR or ARP will offer better handling in close-quarters, such as inside or in other cramped confines.
- Better for defensive applications. Whether you keep your ARP or SBR as a truck gun or in the house for defense, it’ll be more practical for those applications, all else being equal.
- Easier concealment. The smaller, more compact footprint of an ARP or SBR naturally lends itself more readily to concealment than a larger, full-sized rifle.
- More power than a handgun. If it comes down to a rifle-chambered ARP or SBR versus a handgun, the former options will invariably offer much better stopping power than the latter.
Start Your Next Build with a .300 Blackout AR Upper
Ready to start your next AR build and thinking about taking advantage of the benefits of .300 BLK paired with a shorter barrel? Check out our collection of .300 Blackout AR uppers and start there, and if you have any questions about parts, compatibility, or what you’ll need to complete the build, get in touch with us at Sales@MCSGearup.com.