Colt Firearms and other arms makers had previously chambered AR-pattern rifles and carbines in various .30 caliber rounds but encountered problems.

This was particularly noticeable when using subsonic ammunition in conjunction with a suppressor, as short stroking and excessive fouling would occur, similar to that which was seen in the earliest variants of the M16 in Vietnam.

[5] The designers planned several cartridges primarily for the M4 and M16 during load development that not only satisfied the ballistic requirements, but also ensured mechanical reliability with only a simple barrel change necessary for complete conversion.

[8] In July 2015, the Netherlands' Defense Material Organization issued a tender for 195 carbines chambered in 300 BLK on behalf of the Dutch Maritime Special Operations Force (NL-MARSOF).

The intention was to purchase ball, subsonic, and lead-free frangible cartridges, representing the first formal military adoption of the .300 AAC Blackout.

[9] In December 2016, the NL-MARSOF acquired 195 integrally suppressed SIG MCX carbines fitted with a new folding stock, developed for use with ballistic visor helmets, chambered in .300 AAC Blackout, becoming the first publicly-known military user of the cartridge.

[12] In May 2022, United States Special Operations Command selected SIG Sauer to deliver its MCX Rattler personal defense weapon, which can be chambered in both 5.56 NATO and .300 Blackout.

300 BLK rounds like the Barnes TAC 110 grain, have "barrier blind" performance, being capable of penetration through several inches of different hard targets.

[citation needed] The .30 caliber cartridge has an 89.1 percent increase in frontal bullet area over the 5.56×45 mm, and so leaves a larger wound cavity in soft targets.

Weapons chambered for the round can be as light, compact, and quiet when suppressed as submachine guns like the 9×19mm MP5, 5.7x28mm FN P90, and 4.6×30mm MP7 while having more energy and accuracy at longer range.

[16][17] Compared to the 6.8×43 mm Special Purpose Cartridge, another round made to have increased stopping power over the 5.56 NATO, the 300 Blackout has different capabilities.

The 6.8 SPC has a more difficult conversion because it was designed around the obsolete .30 Remington cartridge, requiring a different bolt and decreasing standard magazine capacity.

The 300 BLK was made specifically for ease of conversion, so the standard bolt will work and a magazine can be used to its full capacity, so the only change needed is the barrel and gas system.