.300 Whisper

The .300 Whisper is a rimless, bottlenecked rifle cartridge, one of the Whisper family that J.D. Jones of SSK Industries developed in the early 1990s. It was designed as a multi-purpose round, able to fire relatively light bullets at supersonic velocities and heavier ones, of about 200 to 250 grains, at subsonic velocities. It was originally based on the .221 Fireball case necked up to take a 7.84 mm bullet, and it is also known as .300 Fireball or .300-221.

C.I.P. published a standard for the .300 Whisper in 2009 and last revised it in 2015, the year it first standardised the .300 AAC Blackout, which uses effectively the same case; C.I.P.’s later Blackout drawing lists .300 Whisper among its alternative names. Major makers have since headstamped ammunition .300 Whisper and marked reloading dies and barrels for both names.

Dimensional and pressure figures on this page come from Wikipedia’s infobox, which cites C.I.P. specifications, and are recorded as estimated rather than verified because no independently reachable C.I.P. sheet exists for the Whisper by name. A single bullet weight and velocity are recorded from a COR-BON product page cited by the same infobox; that page is no longer reachable to verify directly, so the figures are recorded as estimated rather than verified. No photograph of a rifle chambered for this cartridge appears on this site.