.338 Whisper

Type

Rifle, subsonic

Place of origin

USA

Production history

Designer

J.D. Jones

Designed

1990s

Manufacturer

SSK Industries

Specifications

Parent case

7 mm BR or .221 Fireball

Case type

Rimless, bottleneck

Bullet diameter

8.59 mm (0.338 in)

Neck diameter

9.11 mm (0.359 in)

Shoulder diameter

11.60 mm (0.457 in)

Base diameter

11.83 mm (0.466 in)

Rim diameter

11.91 mm (0.469 in)

Rim thickness

1.20 mm (0.047 in)

Case length

38.08 mm (1.499 in)

Overall length

67.51 mm (2.658 in)

Ballistic performance

Bullet mass/type	Velocity	Energy
200 gr (13 g) BT	1,077 ft/s (328 m/s)	515 ft·lbf (698 J)
250 gr (16 g) BT	1,040 ft/s (320 m/s)	600 ft·lbf (810 J)
300 gr (19 g) BT	1,050 ft/s (320 m/s)	735 ft·lbf (997 J)

Test barrel length: 12"
Source(s): Cartridges of the World

The .338 Whisper is a wildcat cartridge in the Whisper family, a group of cartridges developed in the early 1990s by J.D. Jones of SSK Industries. Unlike the smaller caliber cartridges in the Whisper family, loads for the .338 Whisper are mainly limited to subsonic velocities.

There are two versions of the .338 Whisper:

A subsonic cartridge is designed to fire its bullets at velocities slower than the speed of sound (1128 ft/s at 70 °F) to avoid the sonic crack caused by the bullet breaking the sound barrier which contributes in large part to the overall noise produced when using a firearm. Subsonic loads are often designed to avoid the turbulent transonic zone entirely. This allows the cartridge to be sound suppressed relatively easily. To ensure terminal performance at subsonic velocities, heavy bullets for the caliber (250-300 grains) (16.20-19.44g) are desirable. Only those .338 based on the 7mmBR case offer meaningful supersonic velocities.A full house load with fast powder can push a 165 grain Barnes bullet out the barrel at 2520fps. Another favourite pick for such an exercise would be the 180 grain Nosler Accubond or the 200 grain Nosler Ballistic tip traveling out at 2200fps-2350fps. Often found to be too explosive in high power rifles, at such moderate speeds the Ballistic Tips provide both expansion and penetration - this combination with excellent accuracy and a high ballistic coefficient. Of course the silent, subsonic loads should be loaded below the speed of sound with preferably the heaviest and longest bullet the .338 calibre has to offer. Currently this is the Berger Hybrid Open Tip Match (OTM)in 300 grains with a BC of 0.818 and a length of 1.820 inches.

"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 cartridges in the Whisper family. For example, .338 Murmur, .338 Phantom and .338 Benchrest. The .300 Whisper (the most popular cartridge of the family) is often called ".300 Fireball" or ".300-221".

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Wikipedia