.510 Whisper

The .510 Whisper is a subsonic rifle cartridge developed by SSK Industries for use in suppressed rifles.[2] It fires a .51-caliber bullet weighing 750 gr (49 g) at roughly 1,050 ft/s (320 m/s).

.510 Whisper
Place of originUSA
Production history
DesignerSSK Industries
Parent case.338 Lapua Magnum
Case typeRimless, bottleneck
Bullet diameter.510 in (13.0 mm)
Neck diameter.549 in (13.9 mm)
Shoulder diameter.587 in (14.9 mm)
Base diameter.587 in (14.9 mm)
Rim diameter.588 in (14.9 mm)
Case length1.875 in (47.6 mm)
Overall length3.34 in (85 mm)
Ballistic performance
Bullet mass/type Velocity Energy
750 gr (49 g) AMax 1,050 ft/s (320 m/s) 1,837 ft⋅lbf (2,491 J)
Source(s): SSK Industries [1]


Despite the large bullet, this round is very quiet, similar to the noise from a .22 Short when used with a suppressor. When used with a very high ballistic coefficient bullet, the round only loses about 100 ft/s (30 m/s) out to over 500 yards. This gives it more downrange energy at that distance than traditional .30 caliber rounds such as the .308 Winchester and .300 Winchester Magnum.[3] Sako TRG-S test rifles have achieved minute of angle, and better, accuracy with this cartridge at 600 yards.[2]

Powders such as H110, 4227, or surplus WC820 are well suited for subsonic loads and give a low standard deviation. Necessary components such as barrels, reloading dies, etc. are available from SSK. Sako TRG-S actions are most often converted to this caliber. The Thompson Center Encore is also suitable, but is rather lightweight for shooting this heavy recoiling cartridge, especially when using 950-grain (62 g) bullets.


The case of the .510 Whisper is based on the .338 Lapua Magnum that has been trimmed down to a length of 1.875 in (47.6 mm) and necked-up to accept a .510 in (13.0 mm) diameter bullet. Neck wall thickness is reduced to 0.013 in (0.33 mm) and a small shoulder is cut into the body for headspacing. Overall length of the loaded round is about 3.34 in (85 mm).

See also


  1. SSK Industries homepage
  2. Barnes, Frank C. (2006) [1965]. Skinner, Stan (ed.). Cartridges of the World (11th ed.). Iola, WI: Gun Digest Books. p. 282. ISBN 0-89689-297-2.
  3. "Whisper cartridges Archived 2007-12-10 at the Wayback Machine" by Lukas Kruesi, New Zealand Guns & Hunting, September/October 2003
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