The .500 Whisper (metric: 13×57mmB[4]) is the first of two .50 in (13 mm) rounds developed by J. D. Jones with a specific focus on the Thumper concept and subsonic use.
[5] Sako TRG-S test rifles have achieved minute of angle, and better, accuracy with this cartridge at 600 yd (550 m).
[3] Powders such as H110, 4227, or surplus WC820 are well suited for subsonic loads and give a low standard deviation.
The Thompson Center Encore is also suitable, but is rather lightweight for shooting this heavy recoiling cartridge, especially when using 950 gr (62 g) bullets.
It can also be viewed as a shortened version of another .510 caliber cartridge based on the .378 Weatherby Magnum, the .500 A-Square (13x73 mm B) developed by Arthur Alphin in 1976.