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.