.
Current Rifle Cartridges
        .30 Remington AR, aka .30 RAR
The .30 Remington AR or 30 RAR was introduced in Sept. of 2009 for use in the new Remington AR-platform rifles called
R15, built by DPMS, a subsidary of the Freedom Group owners of  DPMS, Remington, Bushmaster and other companies.
The .30 RAR cartridge is based on a shortened .284 Winchester case (same as the .450 Bushmaster cartridge) necked
down to  .308" diameter, with a slightly *rebated rim.
Remington is claiming that the .30 RAR in the R15 will have the recoil of a .223 and hit like a .308.
* rebated rim means: The Rim of the case  has a smaller diameter than the case diameter
.
Picture to right of three cartridges:
Left: .30 Remington AR
Middle: 450 Bushmaster
Right: .284 Winchester

The .30 Remington AR cartridge
is based on a shortened .284
Winchester case (same as the .450
Bushmaster cartridge) by necked
down to .308" diameter, with a
slightly *rebated rim.
.