.510 Whisper Subsonic

The .510 Whisper is a specialized subsonic cartridge designed specifically for maximum suppression and terminal performance in a large bore format. Originally developed by J.D. Jones of SSK Industries, the .510 Whisper is based on a .338 Lapua Magnum or .416 Rigby case necked up to accept .510 caliber projectiles, typically used in .50 BMG ammunition. Its primary purpose is to deliver massive subsonic energy with minimal noise when fired through a suppressor, making it ideal for covert, tactical, or specialized hunting applications.

Subsonic loads for the .510 Whisper typically use 750-grain to 950-grain bullets, often match-grade .50 BMG projectiles, kept below the speed of sound (~1,050 fps). At these velocities, the cartridge delivers up to 1,650 foot-pounds of energy, far exceeding traditional subsonic rounds like .300 Blackout. This makes it highly effective on large game or targets where deep penetration and energy retention are critical.

Key considerations for reloading include the use of slow-burning powders such as Hodgdon H4198, IMR 4198, or Accurate 1680, depending on case capacity and barrel length. Because of its large case size, powder selection and charge weight must ensure safe and consistent ignition at low pressures. Handloaders must also carefully manage bullet seating depth and crimp to ensure uniform performance.

Barrel twist rates are usually 1:15" or faster to properly stabilize these long, heavy bullets at subsonic speeds. Given the projectile's size, proper suppressor alignment and durability are also important due to the high bore diameter and energy transfer.

The .510 Whisper remains a niche but formidable subsonic cartridge, favored by specialized shooters seeking extreme quietness without compromising on terminal effectiveness. Though it requires custom rifles and handloading expertise, its performance potential is unmatched in the subsonic realm.