The .30 Remington AR cartridge was created in 2008 by Remington Arms to fill a perceived gap in performance on large game between the .223 Remington and larger cartridges such as the .308 Winchester. Design of the cartridge is considered a joint effort between companies under the "Freedom Group" name through a private equity firm and included such companies as Bushmaster, DPMS and Remington itself. It is a rebated rim cartridge designed to fit Remington's R-15 semiautomatic hunting rifle. It was designed to fit the dimensional constraints of the AR-15 magazine and is based on a modification of the .450 Bushmaster, which in turn was based on the .284 Winchester.
Starting with a .450 Bushmaster case, Remington trimmed the length to 1.525" from the original 1.7" and necked it down to accept a conical .308" diameter bullet with a 25 degree shoulder. The rim size is .492" and because the round generates 55,000 psi, Remington opted to use a .308 rifle bolt in a 5.56 sized rifle for increased case support. The rim was widened from the .473" of the parent case to prevent the use of a weaker .450 Bushmaster bolt with this cartridge. With a 150 grain bullet, the round travels at 2575 fps.
Performance tests between the .30 RAR and the .308 Winchester show that while the .30 RAR does have a good muzzle velocity, the energy it is capable of delivering on target at around 400 yards decreases significantly. Combined with the poorer ballistic coefficients of the lighter projectiles (.267 for the 125 grain Core-Lokt), this makes the .30 RAR a cartridge suited to ranges around 300 to 400 yards, although this could be extended with projectiles of higher ballistic coefficient (.341 for the Speer TNT 125 grain). A side effect of the short, wide case has meant that the Remington R-15 Rifle which was designed alongside the cartridge uses a four-round, single-stack magazine.
