It is a rebated rim cartridge designed to fit Remington's R-15 semiautomatic hunting rifle.

Starting with a .450 Bushmaster case, Remington trimmed the length to 1.525 in from the original 1.7 and necked it down to accept a conical .308 in diameter bullet with a 25-degree shoulder.

[4] The rim was widened from the .473 in of the parent case to prevent the use of a weaker .450 Bushmaster bolt with this cartridge.

[6] 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 can be extended with projectiles of higher ballistic coefficient (.341 for the Speer TNT 125 grain).

[citation needed] A side effect of the short, wide case is that the Remington R-15 rifle, which was designed alongside the cartridge, uses a four-round, single-stack magazine.