Everyone loves America’s Rifle for competition, long-range shooting, and hunting. It’s modular, configurable, and endlessly expandable.
It’s also available - and can be built from the ground up - in a wide range of calibers that are perfect for defensive applications.
And, with a short barrel, a lightweight build, a WML and a red dot sight, an AR platform can be perfect for defense, just as much as it is for hunting or competition.
So, let’s cover a build with a 300 Black upper - and other cartridges that are great to protect the homestead.
300 Black Uppers
The .300 Blackout is a unique cartridge and one that’s only been around for 10 years or so. Here’s what you need to know: it’s basically a 5.56 cartridge that’s been widened to accept a .30 caliber bullet.
As a result, .300 Blackout results in a substantially higher stopping power than 5.56. Muzzle energies for the former can reach nearly as high as 1,700 ft-lbs, whereas for the 5.56, even powerful loads hit around 1,410 ft-lbs on the high end.
This makes .300 Blackout, especially when paired with an appropriate bullet, an excellent cartridge for defensive applications. It also happens to be suitable on game such as deer and hogs.
One of the other great things about building with a 300 Black upper is that a lot of the parts for a 5.56 rifle will work with a .300 Blackout build - like the lower and in some instances, even the BCG and magazines.
Another great thing about building with a 300 Black upper is this: there are a lot of subsonic rounds available, and the cartridge is designed to perform well from short barrels, making it perfect as an AR pistol caliber, as well as for suppression.
The one tradeoff is that .300 Blackout has a pretty sloppy trajectory, so past 100 yards, performance drops off pretty badly.
7.62x39 Uppers
In terms of muzzle energy, the 7.62x39, also known simply as the 7.62 Soviet, performs very similarly to .300 Blackout. The two cartridges are fairly similar in size, too.
Depending on load data, the 7.62 Soviet cartridge will offer somewhere around 1,400 and 1,700 ft-lbs of muzzle energy, putting it fairly on par with the .300 Blackout - the thing is you’ll be more limited in terms of bullet weights, usually between 120 and 125 grains.
However, at close ranges, the 7.62 offers a lot - it hits hard and produces low recoil, just like the .300 BLK - but unlike the .300 BLK, if you build with a 7.62x39 upper, you might be able to get ammo a little cheaper.
Also, both have pretty sloppy trajectories, so keep engagement ranges close. Like .300 BLK, this is potentially a good caliber for hunting small and medium game, too.
9mm Luger
If you want to build a pistol caliber carbine for defensive purposes, it’s really hard to look past a 9mm build.
This is the king of pistol cartridges and has enjoyed well more than 100 years of service. There are lots of great reasons to love this as an AR cartridge, too.
One is low recoil. It produces about the same recoil as .223, which makes it a mild shooter, especially out of a gas carbine with the right buffer weight.
Then we can consider stopping power. Although lower, unequivocally, than rifle cartridges, 9mm Luger still produces close to 500 ft-lbs of muzzle energy, making it ideal at close ranges for defensive applications. Only look at the popularity of the MP5 for evidence.
Another two are the wide availability and low cost. Every gun shop stocks 9mm Luger and usually prices are fairly competitive, even in the modern era. You can mag dump a whole bunch of 9mm during a prolonged range therapy session and if you buy smart it won’t hurt your wallet. With a good bulk deal, you can sometimes get 9mm for less than a quarter a round - and maybe even better than that.
Lastly is the compact nature. Building a carbine-length AR here is a good bet and it will be light and compact, not to mention that 9mm usually performs well from a short barrel - making the platform suitable for close-quarters engagements.
.50 Beowulf
This is the biggest and baddest of the cartridges on this list, and it fires the heaviest bullet of all of these, weighing up to 400 grains.
Even though it’s not the fastest one here (1,900 FPS or so) it pulls by far the greatest muzzle energy, at 2,300 ft-lbs or so.
This cartridge is designed for security checkpoints and for penetrating automobile glass and body panels with minimal deflection.
For comparison, the .50 Beowulf performs similarly to the old black powder .45-70 Government cartridges that were widely used in the west at the turn of the 20th century.
If your goal is maximal penetration and stopping power at close ranges, then .50 Beowulf is the cartridge to beat, and the best one on this list.
Just be ready for it, because recoil can be rough, between 25 and 30 ft-lbs, and ammo can be pretty expensive - but other than that, it’s a great defensive cartridge with next-level power.
Getting Started with Complete AR15 Uppers
Last but not least, it’s worth a note that a 556 upper doesn’t result in low-quality defensive build, by any stretch. The 5.56x45mm NATO cartridge still deserves a lot of credit for its long-distance performance, low-recoil, low cost, relatively high sectional density, and wide availability.
With that said, regardless of the caliber you’re looking for to complete your build, we carry what you need, with a full line of complete AR15 upper receivers (including AR pistol uppers and parts). We also carry build kits, lower parts kits, and sundry parts such as barrels, handguards and rail systems, charging handles, and more. Take a look through our catalog and contact us if you have questions about caliber selection at Sales@MCSGearup.com.