5.56 NATO vs .300 Blackout: Which Should You Choose?
Woody's answers are based on published federal and state law. Not legal advice. Consult a licensed attorney for your specific situation.
Choose 5.56 NATO for versatility, longer range, and cheaper ammo. Choose .300 Blackout for suppressor use, subsonic capability, and close-quarters performance.
How This Affects Your Shooting
The choice between 5.56 NATO and .300 Blackout fundamentally comes down to your intended use case and barrel length preferences. Both cartridges work in AR-15 platforms with only a barrel change required, making this decision purely about ballistic performance rather than major platform differences. Your suppressor plans and typical engagement distances will drive this choice more than any other factors.
The Detail
The 5.56 NATO cartridge excels in versatility and established performance across different barrel lengths. It maintains effective velocity even from shorter barrels, though it really shines with 16-inch or longer tubes where you can fully capitalize on its flatter trajectory and retained energy at distance. The cartridge offers abundant ammunition choices from multiple manufacturers, keeping costs reasonable and ensuring availability during shortages.
.300 Blackout was specifically designed to maximize performance from shorter barrels while offering genuine subsonic capabilities when suppressed. The heavier projectiles, typically ranging from 110 to 220 grains, deliver substantially more energy transfer at close range compared to 5.56. When you're running subsonic loads through a suppressor, .300 Blackout becomes genuinely hearing-safe in a way that 5.56 simply cannot match.
The practical differences become stark when you examine real-world applications. 5.56 NATO maintains supersonic velocity well past 400 yards from most barrel lengths, making it effective for precision work and longer engagements. .300 Blackout drops to subsonic velocities much sooner, limiting its effective range to roughly 200-300 yards with supersonic loads, though it hits considerably harder within that envelope.
Suppressor performance represents the most significant differentiator between these cartridges. While you can suppress 5.56 NATO effectively, it remains quite loud due to the supersonic crack and requires robust suppressor construction to handle the higher pressures and temperatures. .300 Blackout subsonic loads eliminate the sonic crack entirely, creating a genuinely quiet shooting experience that opens up training opportunities impossible with 5.56.
Build Impact
If you're building a dedicated suppressed SBR or pistol, .300 Blackout makes compelling sense for the subsonic capability and better short-barrel performance. For a general-purpose rifle or anything over 14.5 inches, 5.56 NATO offers better versatility, cheaper practice ammunition, and superior long-range capability.