5.56 NATO vs. 300 Blackout

The 5.56 NATO cartridge (and it's commercial sibling, .223 Remington) is the most popular AR-15 caliber. But 300 Blackout, a radically different round, is the second most popular AR-15 cartridge -- and for good reason. So, what's the difference between these two? Let's find out.

5.56 NATO vs. 300 BLK Specifications

Just how different are 5.56 NATO and 300 Blackout? Let's compare specs, then we'll get into velocity and energy comparison between each cartridge's loads.

300 BLK Specifications

• Bullet Diameter: 0.224"
• Rim Diameter: 0.378"
• Case Length: 1.760"
• Overall Length: 2.26"
• Chamber Pressure: 55,000 PSI

5.56 NATO Specifications

• Bullet Diameter: 0.308"
• Rim Diameter: 0.378"
• Case Length: 1.368"
• Overall Length: 2.26"
• Chamber Pressure: 60,916 PSI

Key Differences & Similarities

The big difference between 5.56 NATO and 300 Blackout are their bullet diameters, which place each cartridge in entirely different classes. The 5.56 round uses a .22-caliber bullet, while 300 Blackout uses a .308-caliber bullet.

Despite this, both cartridges are, in fact, physically similar. Both rounds use the same casing -- 300 Blackout simply cuts down the 5.56 casing and widens the neck to accommodate the bigger bullet. 

Both cartridges also produce similar chamber pressures, and their overall lengths are identical. That last part's by design: The 300 Blackout round was meant to work with 30-round 5.56 NATO magazines, something no other .30-caliber cartridge offers in the AR-15 platform.

Reusing the 5.56 casing allows 300 Blackout to work with the AR-15's standard bolt carrier group, and its upper and lower receivers (all other .30-caliber cartridges must be chambered in the larger AR-10 platform).

5.56 NATO vs. 300 BLK Performance

Given that 300 Blackout is essentially a 5.56 casing propelling a .30-caliber bullet, you might expect its ballistic performance to be similar to 5.56 NATO. You'd be half right. 

The supersonic 300 BLK cartridge produces muzzle energy that's similar to 5.56 in certain configurations, but these two rounds afford vastly difference ballistic performance, especially when comparing optimal barrel lengths and subsonics.

Given 300 Blackout and 5.56 were designed to work with difference length barrels, we're comparing both rounds' velocities and energy using 9" and 16" barrel.

5.56 vs 300 BLK: Velocity Comparison (9" Barrels)

Velocities in the chart below are represented in feet per second (FPS).

Cartridge	Muzzle	100 Yds	200 Yds	300 Yds	400 Yds	500 Yds
300 BLK (110 gr.)	2,116	1,858	1,624	1,415	1,242	1,111
300 BLK (220 gr.)	1,000	968	940	914	891	869
5.56 (55 gr.)	2,591	2,252	1,938	1,656	1,408	1,210

5.56 vs 300 BLK: Energy Comparison (9" Barrels)

Energy in the chart below is represented in pound-feet.

Cartridge	Muzzle	100 Yds	200 Yds	300 Yds	400 Yds	500 Yds
300 BLK (110 gr.)	1,094	843	644	489	377	302
300 BLK (220 gr.)	489	458	431	408	388	369
5.56 (55 gr.)	820	619	459	335	242	179

When both rounds are fired from a 9" barrel, 5.56 NATO offers higher muzzle velocity and muzzle energy. It also retains more overall velocity than 300 Blackout, which affords less bullet drop and a flatter trajectory.

But, as distance grows, 300 Blackout retains more energy downrange. Supersonic 300 BLK loads provide more knockdown power than 5.56 at 200 yards and beyond, and subsonic loads afford more power than both supersonic 300 BLK and 5.56 at 400 yards and beyond.

5.56 vs 300 BLK Supersonic: Velocity Comparison (16" Barrels)

Velocities in the chart below are represented in feet per second (FPS).

Cartridge	Muzzle	100 Yds	200 Yds	300 Yds	400 Yds	500 Yds
300 BLK (110 gr.)	2,400	2,117	1,855	1,677	1,406	1,231
300 BLK (220 gr.)	1,060	1,042	1,025	1,010	996	983
5.56 (55 gr.)	3,150	2,520	1,970	1,505	1,165	983

5.56 vs 300 BLK Supersonic: Energy Comparison (16" Barrels)

Energy in the chart below is represented in pound-feet.

Cartridge	Muzzle	100 Yds	200 Yds	300 Yds	400 Yds	500 Yds
300 BLK (110 gr.)	1,407	1,095	841	638	483	370
300 BLK (220 gr.)	549	530	514	499	485	472
5.56 (55 gr.)	1,212	776	474	277	166	118

When fired from 16" barrels, 5.56 NATO provides a flatter trajectory than supersonic 300 BLK up to 200 yards. But approaching 300 yards and beyond, supersonic 300 BLK retains more velocity, producing a flatter trajectory with less bullet drop. It also produces greater energy at the muzzle, and continues to afford significantly more energy than 5.56 NATO, no matter the distance.

Compared to its 9" barrel, subsonic 300 BLK gains little additional velocity when fired from a 16" barrel. But, like its supersonic counterpart, it provides more far more energy downrange than 5.56 NATO, producing more knockdown power than the .22-caliber round at 200 yards and beyond.

5.56 vs. 300 BLK Effective Range

By comparing to 5.56 NATO again, we can find the max effective range of 300 Blackout based on ballistic data. Note this is applicable for supersonic (125-grain) loads only.

The U.S Military calculates the max effective range of 5.56 NATO to be 500 meters. This is based on a 50% hit probability, which guarantees every other round will hit its target at the given distance. At 500 meters, 5.56's ballistic data looks like this:

• 100" of drop
• 41" of drift
• 291 ft. lbs. energy

300 Blackout's ballistic data is comparable to 5.56 at 440 to 700 meters:

• 100" drop (440 meters)
• 41" drift (484 meters)
• 291 ft. lbs. energy (700 meters)

Officially, the U.S. Military has calculated supersonic (125-grain) 300 blackout's max effective range to be 440 meters. That's a loss of just 60 meters compared to 5.56 NATO, while affording far greater energy at that distance.

5.56 vs. 300 BLK Parts Compatibility

Building a rifle or pistol chambered in 300 Blackout is easy. Most of the parts you'll need are the same parts designed for 5.56 NATO or .223 Remington:

• Lower receiver
• Lower parts kit
• Gas block
• Gas tube
• Buffer
• Buttstock
• Buffer tube
• Recoil spring
• Bolt carrier group
• Charging handle
• Upper receiver
• Handguard
• Magazine

The barrel and length of the gas system are the only things exclusive to 300 Blackout. All other AR-15 parts are compatible with this round. If you wanted to, you could simply swap the barrel and gas system length on an existing gun chambered in 5.56 or .223. This would convert it to fire 300 BLK without further modification required.