5.56x45mm NATO vs 300 AAC BLK: Which is Best for You?

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When people try to compare 5.56x45mm NATO with 300 AAC Blackout, they usually approach the discussion in the wrong way, because this is not comparing apples to apples but rather apples to potatoes. It’s not which cartridge is superior to the other, it is which better suits your specific needs. The 5.56x45mm cartridge has been our primary military rifle caliber since the demise of the 7.62x51mm M14 in 1967. While technically it is an “intermediate” caliber compared to the .30-caliber cartridges it has replaced (.30-‘06 and 7.62x51mm), it has proven itself over the last 60 years, which is why we’re still using it. Anyone who thinks the 5.56x45mm NATO is a “poodle shooter” or that it doesn’t perform well against bad guys is living in the past, ignorant of real-world results, and probably thinks .45 ACP is still better than 9x19mm and a shotgun is the best choice for your grandmother for home defense.

5.56x45mm NATO

No, just no to all of that. The military-issued 5.56x45mm first featured a 55-grain FMJ-BT bullet, but that was increased to 62 grains in the 1980s with its NATO adoption. What makes this cartridge effective is its velocity. It is a small, relatively light bullet, but it travels fast, often with a muzzle velocity over or near 3,000 feet per second (fps). This provides a flat trajectory. If you’re not in the military, you can use the latest and greatest bullets which are designed to not just penetrate intermediate barriers but expand in bad guys. The terminal performance with modern expanding bullets is very good. The Barnes copper solid TSX and TTSX bullets are perhaps the best of these, but there are dozens, and actual shooting results (LE and private citizen) have shown they work. In addition to their terminal performance, there’s this—the 5.56x45mm NATO cartridge has minimal recoil. So, it’s easy to shoot and easy to control. Plus, both it and its commercial cousin, the .223 Remington (.223 Rem has the same external dimensions but is loaded to slightly lower pressures) are widely and readily available. The 5.56x45mm NATO is a great general purpose rifle cartridge that works reasonably well for everything short of hunting larger game.

5.56x45mm Advantages

• Widely available, easily found across the country.
• Economical, inexpensive loads are readily available.
• Match, Hunting and Personal Protection loads available.
• Flat trajectory.
• Known for its accuracy.
• Excellent terminal performance for personal protection.
• With the right loads, it can be used at 600+ yards.
• Mild recoil.
• Easy to reload.
• US military and LE standard, so new loads constantly being developed.

5.56x45mm Disadvantages

• Poor performance with subsonic loads.
• As barrel length drops, performance drops.
• Not an ideal choice for large game hunting.
• Terminal performance tends to be velocity dependent.

300 AAC Blackout 

The 300 AAC Blackout, or 300 BLK, is a completely different animal. Predating the 300 BLK by decades are both the .300/.221 Fireball (.300 Fireball) and the .300 Whisper®. The .221 Fireball was wildcatted by necking it up to .30 caliber, probably for metallic silhouette shooting not long after its parent case appeared. The .221 Fireball based .300 Whisper cartridge was developed and trademarked in 1992 by renowned gunsmith (and gunwriter) J. D. Jones. Jones was thinking about the usefulness of the cartridge in single-shot hunting pistols and AR-15s (suppressed and otherwise). He developed the .300 Whisper to be a “dual-purpose” cartridge capable of firing both lighter (110 to 130-grain) bullets at supersonic velocities as well as heavy bullets at subsonic velocities for use with a sound suppressor. For subsonic loads he favored the 0.308-inch 220-grain Sierra MatchKing bullet at about 1,000 fps. The overall length of the loaded cartridge is the same as a .223/5.56. 

Keep in mind, J.D. Jones was a pioneer when it came to subsonic cartridges for use with sound suppressors. He was ahead of the curve. In the 1990s sound suppressors were not nearly as popular or as mainstream as they are today. Neither were AR-15s for that matter. Typically it was small highly specialized military units or government agencies which took interest in his work. That’s where the cartridge stayed for a number of years, a quiet (when suppressed) wildcat cartridge few people had ever heard of. 

I’ve spoken to Kevin Brittingham, founder of Advanced Armament Corporation (AAC) and current CEO of Q (www.liveqordie.com), about the origins of what ultimately became the 300 AAC Blackout cartridge and the famed Honey Badger PDW. “We (AAC) were doing the silencers for the (U.S.) Navy SEALs. That group, along with their cousins in the army had wanted the ability to fire 7.62x39mm through the M4 platform for quite some time. But it’s just not feasible because of the AR mag well. Which led them to .300 Whisper.” said Brittingham. 

He continued, “They loved the concept but couldn’t get the guns to run reliably and wanted us to look at it. This guy was smart enough to understand he really had an ammo problem, so with Remington buying our company he wanted to know if we were interested. They wanted super- and subsonic ammunition, the supersonic having the performance of the AK, and the subsonic being as quiet as we could get it, like the MP5SD.”

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The end result ultimately became the famed 300 AAC Blackout Honey Badger PDW. Remington focused most of their commercial effort on the renamed and SAAMI-approved Blackout’s capabilities for hunting and defense through the use of supersonic ammo. The original supersonic Blackout load featured a 110-grain bullet heading downrange somewhere between 1,900 and 2,300 fps, depending on barrel length. Subsonic ammunition features roughly 200-grain bullets travelling at or above 1,000 fps. Subsonic Blackout has little recoil. Supersonic Blackout has about 25% more recoil than 5.56x45mm NATO.

300 AAC Blackout Advantages

• Dual-Purpose Supersonic/Subsonic capabilities.
• Optimized to work well in very short barrels.
• Subsonic ammunition is very quiet with a good suppressor.
• Supersonic ammunition offers good terminal performance.
• Can feed from standard 5.56x45mm AR mags.
• Subsonic ammunition has very mild recoil.
• Designed to work well in the AR-15 platform.
• Easy to reload.
• Useful for hunting and personal protection.
• New loads constantly being developed.

300 AAC Blackout Disadvantages

• Low muzzle velocity makes it a poor performer at longer ranges.
• Ammunition is more expensive than 5.56x45mm.
• Some guns may not run flawlessly with both Supersonic and Subsonic loads.
• Terminal performance with subsonic loads is similar to handgun loads.
• Heavy match bullets typically used for subsonic loads are very expensive.

But, if you’re trying to fit the 300 AAC Blackout into some sort of traditional rifle cartridge niche, you’re looking at the cartridge from the wrong perspective. Many of the old-school rifle guys I know look at the specs of the 300 AAC Blackout cartridge, squint, frown, and then walk away, muttering. If you compare the specs of the Blackout (in supersonic form) to most standard “rifle” cartridges, it is rather anemic, giving you slightly less bullet speed/weight than a 7.62x39mm, which is no powerhouse. But you’re missing the point. The 300 AAC Blackout cartridge is optimized for a 9-inch barrel. Whether you’re talking AR pistols or short-barreled rifles (SBRs), a lot of AR fans want a gun that is as short as possible. The .223/5.56 though is a cartridge that doesn’t do so well out of super short barrels. A standard 55-grain 5.56 load will do roughly 3,000 fps out of a 16-inch barrel. Shorten that barrel to 7.5-inches (currently the favorite uber-short length), and you’ll be lucky to get 2,200 fps out of most 5.56x45mm loads. That’s a velocity loss of nearly 30% in a cartridge that relies on velocity for its terminal performance as it features a small, light bullet. And the resulting blast and concussion is shocking.

The powder found in the 300 AAC Blackout was specifically chosen so the cartridge would not be handicapped when fired out of short barrels. Another factor in play is bore volume. The bore volume of an 8-inch 300 Blackout is the same as that of a 13-inch barreled 5.56x45mm, and the former is loaded with fast pistol powder, the latter slower rifle powder. When comparing velocity of supersonic Blackout loads through 9- and 16-inch barrels, the 9-inch gun retains 90% of the velocity, while being barely more than half the length. As a “general purpose” cartridge, the 5.56x45mm NATO is arguably superior. It is lighter, has less recoil, is cheaper, more readily available, has a wider range of available projectiles. It is deadly to deer, hogs, and people, and out of rifle-length barrels does everything arguably as well as 300 Blackout short of downing larger game and punching through barriers, as mass wins there, and supersonic Blackout bullets weigh generally twice as much.

If you want an AR pistol or SBR with a barrel length shorter than 10 inches, chances are you’re far better off choosing 300 AAC Blackout than any other cartridge, especially 5.56x45mm, which loses speed drastically in any barrel length shorter than 11.5. Supersonic Blackout ammo was optimized for use in short-barreled ARs and in just about every way crushes the caliber competition when your barrel length reaches single digits. Out of a 5.5-inch barrel, a 110-grain 300 BLK has the same velocity as a 55-grain 5.56 NATO. And if you’re interested in being very, very quiet, a suppressed AR firing subsonic 300 BLK ammunition is as quiet as quiet semi-auto gets, while offering the familiarity of AR controls.

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