| Centerfire rifle|
| United States|
.243 in (6.2 mm)
The 6mm AR is a centerfire wildcat cartridge designed by Robert Whitley for long-range performance in an AR-15 rifle.
6mm AR Wikipedia
The cartridge uses a 6.5 Grendel case that has been necked-down to accept a 6 mm (.243 in.) bullet.
The 6mm AR takes advantage of the wide variety of .243 in. caliber bullets. Slim, long bullets with high ballistic coefficient are ideal for energy retention at long ranges.
It is similar to the 6PDK which also uses a 6mm bullet and a similar muzzle energy and case capacity to the 6mm AR and 6.5 Grendel, in a casing popular for the AR-15, a necked-down 6.8mm Remington SPC casing which does not need special magazines to fit the AR-15.