.300 Whisper is a wildcat cartridge, a completely different round, and is not SAAMI standardized.
300 ACC Blackout comes in both Supersonic and Subsonic version. The official AAC specs state this:
Bullet weight/type
Velocity
Energy
125 gr (8 g) OTM
2,215 ft/s (675 m/s)
1,360 ft·lbf...