The most obvious way to improve lethality or increase a rifle’s maximum effective range is to use a larger cartridge, but that usually calls for a bigger rifle. It’s easy enough to lengthen a commercial rifle’s receiver a fraction of an inch, but, with several million M-16 and M-4 rifles on hand, those hoping to get into the military supply chain needed to do so with a round that fit in a standard Mil-Spec magazine. That set a lot of talented designers and ballisticians to work and produced a whole gaggle of really clever, useful cartridges.
Probably the most successful and popular round is the 6.8mm Special Purpose Cartridge. After the 5.56’s lackluster performance in Afghanistan, in 2001, U.S. Special Operations Command shooters worked to come up with something better that still worked in an M4. They did some experimentation with PPC cartridges, but designers finally settled on the obsolete .30 Remington case, because of its smaller rim diameter. There was enough case capacity to push 110- and 115-grain bullets to velocities substantially beyond what the 7.62X39mm could produce with 123-grain FMJ bullets. Swapping calibers was an armorer-level job that required only a barrel, bolt, and magazine change.
The 6.8mm SPC worked like a charm for close- and long-range engagements, producing far better results than that experienced with the 5.56 mm. Why the round was not adopted by units outside of SOCOM is anyone’s guess. Several U.S. manufacturers started producing commercial ammunition with open-tipped match, polymer-tipped, and hunting bullets, and nearly every AR manufacturer soon had a 6.8 in their catalog. Hunters have found the round perfect for whitetails and other medium-sized game, when the shots fall inside 300 yards. And, while the 6.8 mm SPC is not the U.S. Military’s next service round, it is now firmly entrenched in the AR-15 shooting community.
The round is now the second-most popular AR-15 chambering.One of the more versatile intermediate rounds is the 6.5 mm Grendel developed by Bill Alexander, of Alexander Arms. He took a 6mm PPC case, shortened the neck, moved the shoulder forward, and increased the diameter to take advantage of all those 6.5mm bullets with their superb ballistic coefficients. The end result is a cartridge that can better the 5.56 NATO—or 7.62 NATO for that matter—in just about every category. The Grendel is also a capable competition round, one with the reach to compete at the 1,000-yard line, something the 6.8 mm SPC cannot do. With properly constructed bullets, it is a great varmint or medium-game hunting round.