Current Rifle Cartridges
300 Whisper
The 300 Whisper was developed as a wildcat cartridge by J.D. Jones of SSK Industries for the Thompson/Center
Contender single shot pistol or rifle. It was made by necking out the .221 Remington Fireball from .22 caliber to
.300 caliber,which also reduces the case neck angle from 29 degrees to 23 degrees.
It was later produced by the Cor-Bon Company, and in 2013 by the Hornady Company for the AR-15 platform for tactical
entry operations by military & police.
Although the .300 Blackout  and .300 Whisper are very similar, there is a difference in angles and preseures. You should
not fire a .300 Blackout in a firearm chambered for the 300 Whisper as they may have slight variations in chamber
dimensions, which could lead to unsafe high preserves. I can’t speak for the Hornady production.
Pictured at left and for sale is the
300 Whisper by Hornady, with
proper "300 Whisper" Head Stamp.
Loaded with a 208 grain, "AMAX"
projectile "SUBSONIC"
only 1,000 Feet per Sec.

On the Picture on the right side
for size comparison
on Left: .300 Whisper
on Right: .221 Remington Fireball