.300 Whisper

The .300 Whisper (also known as .300 Fireball or .300-221) is a wildcat cartridge in the Whisper family, a group of cartridges developed in the early 1990s by J.D. Jones of SSK Industries. It was developed as a multi-purpose cartridge, capable of utilizing relatively lightweight bullets at supersonic velocities as well as heavier bullets (200-250 grains) at subsonic velocities.

The .300 Whisper was originally based on the .221 Fireball case necked up to 30 caliber however, avid reloaders have found the .223 Remington or 5.56 X 45 mm NATO works well when shortened and resized to 30 caliber. Firing in the .300 Whisper chamber results in a slightly sharper shoulder. Magnum pistol powders such as H110 work well for subsonic loads. Sierra 240 grain (16 g) jacketed bullets work well if the barrel has a 1:8 twist. Barrels with a 1:10 twist will stabilize 220 grain (14 g) bullets at subsonic speeds. 125 grain (8 g) bullets will reach 2400 ft/s (730 m/s).

There are a few points to be considered regarding the utility of the .300 Whisper:


 * 1) Supersonic loads are capable of matching ballistics of the 7.62x39mm and the .30-30 Winchester, making the .300 Whisper very capable as a short range deer hunting cartridge.
 * 2) The use of heavy bullets, along with the low powder weight and small case capacity, make the .300 Whisper ideal for use with sound suppressors. These subsonic loads offer energy levels similar to that of the popular .45 ACP pistol cartridge, but range is substantially increased due to the longer, more efficient 30 caliber bullet.
 * 3) Cases for the .300 Whisper can be formed from common and plentiful .223 Remington brass by sizing and trimming to length. However, J.D. Jones has recommended against this, citing the difference in case thickness at the neck (compared to the .221 Fireball) as a potential issue. This problem can be exacerbated when military 5.56x45mm cases are used.
 * 4) Perhaps most importantly, any firearm with a .223 Remington bolt face can be converted to .300 Whisper by re-barreling the action. As such, the .300 Whisper works well in AR-15-based rifles, especially when some type of gas regulator is installed.

In addition to special applications in suppressed firearms, the .300 Whisper has become popular with metallic silhouette shooters due to its low recoil, good long range performance, and very high accuracy.

Trademark
"Whisper" is a registered trademark of SSK Industries. In order to sidestep this branding (and/or any licensing fees required to use the "Whisper" name legally), other manufacturers tend to use different names for the same cartridge, such as ".300 Fireball" or ".300-221", both based on the .221 Fireball parent case.