The AR-15, also called the Modern Sporting Rifle or the Black Rifle, is generally chambered for the .223 Remington or the closely-related 5.56 NATO cartridges. An AR-15 variant is a similar rifle in a different caliber. Since ARs have two sections, an upper and a lower, it is possible to swap in a different upper (and sometimes also a different bolt and/or magazine) in order to fire a different caliber of ammunition. There are many AR-15 variants. Which are best for home defense?
I should begin by saying that an AR of any type is not necessarily the best choice for everyone. If you would mostly be using a firearm to defend yourself within your home, I think you might be better off with a pistol or a pistol-caliber carbine. A pistol can be conveniently kept in a small safe by your bedside. It’s also convenient to carry a pistol while you are working or relaxing in your home. Rifles are best for use outdoors, where their effectiveness at extended ranges is important. Indoors, the noise of a rifle shot is louder and even more likely to damage hearing. However, you should have a pair of ear muffs for hearing protection by your gun regardless of whether it is a pistol or long gun, regardless of where you might be shooting.
The .223/5.56 caliber is effective in fighting off an assailant, as proven by its use by the U.S. military for many years now. However, the bullets have a limited weight (up to about 75 or 77 grains, at most), and the range for greatest terminal effectiveness is significantly less than some of the variants.
The 300 BLK fires subsonic rounds of up to 220 grains or so, as well as supersonic rounds of up to 125 grains. The idea was to duplicate the ballistics of the ammunition used in the AK-47 (7.62×39), while also offering effective suppressed fire.
This cartridge was designed so that an AR-15 (or military M4 carbine) could be converted to the caliber with only a swap of barrels (or uppers). The standard bolt and magazines for the 5.56 caliber will work with this ammunition.
For home defense, the upside is that suppressed 300 Blackout ammo is quieter than suppressed 9mm rounds. And then you have the option of shooting supersonic ammo with an effective range of about 300 yards. Ammunition is more widely available now than ever before, and its reliability and performance seems to have approved.
On the downside, you need a suppressor to take full advantage of the 300 Blackout platform. And in order to get good suppressed effectiveness, you’ve traded away a great deal of range.
Warning: The ammo from the 300 BLK can be mistakenly loaded into a .223/5.56 rifle, and vice versa, resulting in a dangerous situation. Firing the wrong ammo in a gun can result in serious injury or death. And that’s another downside of this caliber.
This caliber is renowned for its effectiveness when fired from the AK-47 rifle. The combination of rifle and ammo is very reliable, though not so accurate. Recoil is modest, but effective range is limited. The short 7.62mm projectiles have poor ballistic coefficients, and the short cartridge limits the amount of gun powder and therefore the muzzle velocity. But for close to medium ranges, it’s sufficiently deadly.
Now, as an AR variant, the same caliber ammunition offers a different story. You can find an upper or a complete rifle that is reliable and accurate, but it’s a chore. This ammo was not designed for the AR platform and it shows. If you have an accurate and reliable AR in this caliber, good on you. But you need a compatible bolt and magazine, not just a barrel or upper.
On the upside, 7.62×39 ammo is cheap and plentiful. And once you have the rifle working well, you’re all set.
This caliber would be an interesting choice for home defense, though it is certainly not for everyone. In a suppressed rifle with a short barrel, the 458 SOCOM offers unbeatable terminal effects: a bullet of 400 to 600 grains at around 1000 ft/s hits very hard. The subsonic rounds are low pressure and are easily suppressed. Recoil is not so different from the mild shooting 7.62×39. However, the recoil impulse from the very heavy slow bullets are more of a push than a snap. A home invader who gets hit, center-of-mass, with one of these pills is done.
The ammo is also available in supersonic loadings, with bullet weights still quite heavy at 250 to 400 grains. However, the recoil is in the same range as a .308 rifle shooting loads with muzzle energy of 2100 to 2400 ft-lbs. And that’s a lot of power for a home defense gun. Then, too, the velocities are mostly sub-2000 ft/s. So the range is limited to a couple of hundred yards. I know that the supersonic loadings are popular with AR aficionados. But for practical use in home defense, the subsonics are the way to go.
Compared to the 300 Blackout, the 458 SOCOM gives you only 10 rounds in a 30-round 5.56 magazine, whereas the 300 BLK gives you a full 30 rounds. But the 458 hits much harder.
The 6.8 SPC gives you heavier bullets than the 5.56, at decent velocities, resulting in greater range and greater terminal effects. The recoil is moderate and the round works just fine in short barrel rifles. You don’t really have a good option for heavy slow suppressed ammo, but supersonic ammo can be suppressed (just not as well).
If you have to choose between the 5.56 and the 6.8, the latter has every advantage, until you consider price and availability. The 6.8 SPC ammo is still not widely available in stores; you’ll need to buy online. And it’s significantly more expensive than 5.56 ammo.
Once you have the ammo, though, the 6.8 SPC is highly effective, reliable, and easy to shoot. It’s a good choice for an AR variant for home defense, especially if you live in a very rural area.
Discussions online, as to which variant is better, 6.8 SPC or 6.5 Grendel, are endless. Whenever some newbie asks that question, one of the first responses is usually something like: “Nooooo! Not this again!” The two cartridges are similar in many ways and have many of the same advantages, especially when compared to the .223/5.56.
The 6.5 Grendel really shines in long range shooting with a longer barreled AR (18 inches or more). It does handle heavier bullets than the 6.8 SPC at decent velocities. The 6.5mm bullets have much better ballistic coefficients than the other calibers discussed above. That means you can reach out and touch someone at much greater ranges, without suffering the recoil and muzzle blast of a .308 or similar caliber. It’s arguably the best long range cartridge in the AR-15 platform.
Downside is that the ammo is expensive and the number of rifle or upper manufacturers is still limited. Like the 6.8 SPC, you really need caliber-specific magazines and a well-designed caliber specific bolt as well as a new upper.
For a short-barreled and suppressed weapon, I’d favor the .300 Blackout. For home defense, you probably don’t need to hit targets beyond 300 yards. And the 300 BLK suppresses well. Getting a rifle that runs both subsonic and supersonic ammo well is tricky. But once you have a reliable rig, you’re good to go. Ammo is getting cheaper and more plentiful in this caliber.
For an unsuppressed weapon for use in a very rural area, I’d go with the Grendel. It has the range that you may need, in a lightweight low-recoil weapon. The ammo is not so widely available. But once you stock-up, you are ready for the S to hit the F.