A wildcat cartridge developed by J.D. Jones of SSK Industries as part of the Whisper family of subsonic cartridges. Fires heavy bullets at subsonic velocities, optimized for suppressed use. At .510" bore diameter it delivers substantial terminal energy even below the sound barrier — typically 1,000–1,600 ft-lbs depending on bullet weight.
Type: Rifle
Introduced: 1992, United States
Standardization: Wildcat
Bullet diameter: 0.51" (12.95 mm)
Max pressure: 45,000 PSI
Rim type: Rimless
Primer: Large Rifle
Muzzle velocity: 920–1050 fps
Muzzle energy: 1075–1640 ft-lbs
Effective range: 150 yd
Common bullet weights: 570, 600, 650, 700, 750 gr
Primary use: Specialty, Self Defense, Hunting
Production status: Limited
History: J.D. Jones developed the Whisper cartridge family at SSK Industries beginning in the late 1980s to maximize suppressor effectiveness by keeping projectiles subsonic. The .510 Whisper is the large-bore flagship of the family. Jones also created the .300 Whisper, which became the commercial .300 Blackout. The Whisper series directly influenced the modern subsonic rifle cartridge movement.