Fenix Ammunition: A Ballistic Comparison of 5.56x45mm vs. .300 AAC Blackout

This article comes from Fenix Ammunition and is reprinted with permission gained via Twitter DM on 2/17/21. Fenix Ammunition has recently made the news because it forces anyone wishing to do business with them to check a box certifying that they did NOT vote for Joe Biden. It is largely symbolic but I also think it does make the person who did vote for them think harder about their choice. They have a great Twitter and they are outspoken Patriots. Check out their products here and, if you order anything, let them know we sent you!

Picture courtesy of The Truth About Guns.

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The .300 AAC Blackout (aka .300 BLK, 300 Blackout, and 7.62 x 35mm) cartridge was developed by Advanced Armament Corporation and submitted for standardization to the Sporting Arms and Ammunition Manufacturer’s Institute (SAAMI) and approved in 2011. The .300 BLK was developed in response to requests from the military for a standardized cartridge with more energy on target and “punching” power than the standard 5.56x45mm NATO cartridge at close and medium ranges, while maintaining the standard 30 round magazine of the government issued M4/AR-15 rifles.
Advanced Armament was able to achieve this by shortening a .223 Remington/5.56mm brass case and then “necking” up the brass case to utilize a larger, heavier .308”/7.62mm diameter projectile. Since the .300 Blackout shares the same case head dimensions as the .223 Remington / 5.56mm NATO cartridge, it allows use of the same bolt carrier group and magazines as a standard M4/AR-15, making conversion as simple as swapping the barrel and muzzle device. This has made the round extremely popular with the civilian AR-15 market for target shooting, hunting, and defensive use.
Despite reams of data, there is much debate regarding the ballistic advantages and disadvantages of 5.56x45mm as compared to .300 AAC Blackout.  In this article, we will discuss several distinct advantages to .300 Blackout primarily in Close Quarters Combat (CQB) and defensive situations.
Projectile Frontal Area
A major advantage of .300 Blackout is the increased “Frontal Area” provided by the larger diameter .308” caliber projectile.  Frontal Area is the total area of the circumference of the cylinder represented by the projectile facing the target.

All things being equal (velocity, projectile expansion upon impact, etc.), projectiles with a larger frontal area crush/tear more tissue than those with a smaller frontal area, thereby increasing the capacity for wounding.  To provide some comparison, the difference in frontal area between a .308” projectile and a .224” projectile is much larger than the difference between .45 ACP and 9mm.

• For example, going from 9mm (0.354″) up to .45 ACP is a 27.2% gain in frontal area
• Going from .224” to .308” is an 89% gain in frontal area

MAXIMUM EFFECTIVE RANGE
The US Military rates the Max Effective Range of the M4 as 500 meters for a point target.  Using 500 meters as a benchmark, a NATO standard 5.56x45mm M855 projectile fired at 2,900 FPS will have 100 inches of drop, 41 inches of drift, and 291 ft.-lbs. of energy at that distance.
In contrast, a .300 Blackout 125 grain projectile at 2,220 FPS has:

• 100 inches drop at 440 meters
• 41 inches drift at 484 meters
• 291 ft-lbs of energy at 700 meters.

What does this illustrate?  By the math, .300 Blackout will experience greater drop due to being fired at a slower velocity, thereby increasing the amount of holdover required to hit a target at the same distance.  However, due to the increased weight of the projectile, it will provide more kinetic energy on target at 500 meters and will provide the same kinetic energy as the 5.56 M855 cartridge out to 700 meters.
While the 300 AAC Blackout has far more energy, the military’s primary statistical benchmark is a calculation known as “Hit Probability”. Hit Probability removes kinetic energy from the equation and focuses solely on the likelihood of connecting with a target at a known distance.  The primary factors affecting hit probability include the impact of wind and barometric pressure on the projectile in flight, and the loss of velocity in flight resulting in the projectile drifting from the point of aim.
If we consider that the drift and drop range is correlated with hit probability, the US Military has calculated that a .300 Blackout 125gr cartridge fired at 2,200 FPS has an equal probability of hitting the target at 462 meters compared to the 5.56 NATO M855 projectile at 500 meters, a loss of only 38 meters.
While this APPEARS to be an advantage in favor of 5.56x45mm, the US Military has also shown through extensive data analysis that the average engagement for infantry units is LESS than 300 meters.  Therefore, maximizing ballistic energy and hit probability INSIDE 300 meters should be considered the primary factor for choosing a caliber for the vast majority of military operations.

Using 300 meters as the benchmark, we can compare the energy of the two cartridges assuming identical atmospheric conditions:

 
At 300 yards, the .300 Blackout projectile retains 154 ft.-lbs. GREATER kinetic energy than the 5.56 NATO projectile, equal to a 45.97% increase.  At 50 yards, the difference is 248 lb.-ft. or a 34.73% advantage.  99.9% of civilian defensive firearm encounters happen within 15-25 feet, making close-range ballistic energy even more important.
IMPACT OF BARREL LENGTH ON CARTRIDGE PERFORMANCE
One of the problems facing the development of the 5.56x45mm NATO cartridge was the initial use of 20” and 24” barrels for the M16A1 platform.  As time has progressed, the military has moved increasingly toward shorter barrels due to the tight spaces soldiers face in urban warfare settings.  Additionally, concerns about hearing loss and Traumatic Brain Injury (TBI) from repetitive automatic fire has led to an increased use of sound suppressors on the M4 rifle.  In order to prevent soldiers from having to wield awkwardly long weapons, it has become necessary to shorten barrel lengths to provide a compact weapon system suitable for CQB environments.
Unfortunately, there is no free lunch.  Shortening barrel length reduces the muzzle velocity of the 5.56 NATO cartridge significantly, reducing its maximum effective range and INCREASING the amount of bullet drop / wind drift experienced at longer engagement ranges.  The table below illustrates a comparison