We often scoff at the new chamberings offered by ammunition manufacturers. “Solutions to nonexistent problems” we say. Sometimes, that is true. More often, the puzzling profusion of the new offerings has to do more with legal regulations than with performance – 45GAP and 9×21 are the prime examples of such developments. They were brought up to approximate the performance of 45ACP and 9×19 Luger without being prohibited military ammunition.
At other times, flatter trajectory combined with lower recoil are the goal. 25-06 and 7-08 are such derivations from 30-06 and 308 respectively. Yet another reason for new cartridges is the use in different style of firearm. For example, 45 Auto Rim adapted 45ACP to revolver use without requiring moon clips. 458SOCOM provided 45-70 Government and 450 Marlin performance in a smaller package adaptable to the low-recoil AR15 platform.
Sometimes, the logic of introducing apparently competing cartridges of similar dimensions and performance isn’t very obvious. 9mm Luger, itself derived from 7.65mm Luger by necking up to increase payload, competed against 9mm Steyr, Glisenti and Mauser. The Luger cartridge won mainly on technical merits, though being the first out of the gate also helped.
Recently, we’ve seen a similar profusion of short 30-something caliber cartridges crowd into the realm previously occupied by 7.62×39 Russian and .300 Whisper. Neither of those rounds is a great fit for the AR15, and so alternatives were developed. These new rounds, mainly 300 Blackout and 338 Spectre, both try to improve on the existing rounds while preserving maximum compatibility with .223 Remington and 6.8mm SPC.
300 Blackout is a clever design that fits 30 7.62mm cartridges into a standard .223 magazine. With more than double the bullet weight of the .223, it is notably more effective and equals the AK cartridge in effect. With shorter rifles and sound suppressors becoming more popular, it promotes reliability by having the same gas port pressure in standard and subsonic loads. In effect, it approximates both the 7.62×39 Russian and the dedicated subsonic 9×39 Russian, though with a smaller, lighter bullet.
Designed to fit 25 rounds to a standard 6.8SPC magazines, 338 Spectre is optimized around subsonic performance, though it also offers a number of high-velocity supersonic loads. Slightly inferior to 300 Blackout in supersonic performance, 338 beats it and the Russian 9×39 decisively in suppressed use. Since the muzzle velocity is limited by having to stay under the speed of sound, this cartridge uses extremely heavy bullets. 300BLK tops out at 220 grains, 9×39 at 250, while 338 Spectre launches 300 grain low-drag projectiles. Having by far the greatest sectional density, it also retains velocity and energy much further downrange. That extra punch means superior penetration, a useful feature in the day of ubiquitous body armor. 338 Spectre is a lower pressure cartridge than 300BLK by design, so instead of requiring a dedicated rifle sound suppressor, it can utilize much lighter and smaller 9mm pistol suppressors.
When new ammunition designs come out, it’s difficult to predict which rounds will become and remain popular. The much-maligned 40S&W is popular despite the naysayers, while initially lauded 44 Automag is long gone. Given the financial and technical hurdles in introducing new chamberings, it is not surprising that the most promising rounds have a number of compelling reasons behind their introduction. Not all of these reasons are obvious, but they do exist.