.300 Whisper / .300 AAC Blackout
Date: Apr 15 2020
In the early 1990s J.D. Jones of SSK Industries began developing a wildcat cartridge (at the request of US military Special Forces) that became known as the .300 Whisper. It was based on the .221 Remington Fireball case necked to .30 caliber and had an overall length of 2.260 inches - same as the .223 Remington - allowing it to function in the AR-15 rifles and magazines. The purpose was a sub-sonic cartridge with long heavy bullets featuring a high ballistic coefficient that was effective at 200 yards while being essentially silent when suppressed. The Whisper also offered the versatility to push 125- grain bullets at 2,250 fps, which significantly extended its range, but at the cost of increased sound.
Although Hornady eventually offered .300 Whisper factory ammunition, it was a proprietary cartridge. In 2011 The Freedom Group and Advanced Armament Corporation (AAC) announced the .300 AAC Blackout, a standardized commercial version of the .300 Whisper. Whisper’s built after 1999 were dimensionally identical to the .300 Blackout and are fully interchangeable; however, the latter features a .015-inch longer chamber throat.
In developing loads for this cartridge, some published data required an excessively compressed powder charge, which bulged the case body just below the shoulder when seating bullets, effectively ruining the case. None of the loads presented here are excessively compressed.
When loading for AR-15 rifles, a small base sizer die is suggested, and bullets should be crimped in place.
Virtually all powders tried gave the best accuracy and most consistent velocities when used in conjunction with standard Small Rifle Primers, with the only possible exception being Hodgdon Lil’Gun powder when used with 110- to 130-grain bullets.
When assembling sub-sonic ammunition, small changes in powder charges, powder lot numbers, primers and cases can change velocity, sometimes significantly. The point being, when loads are targeted to reach just under sub-sonic velocities, any small change may bump velocities to supersonic speeds. A chronograph will prove a great aid for fine tuning handloads.
Top performing powders included Hodgdon H-110, Lil’Gun; Winchester W-296; Accurate AAC-9, AAC-1680, AAC-2015 and Alliant 2400.
When loading bullets ranging in weight from 168 to 225 grains, avoid loads that drop velocities below 900 fps, as some powders may not produce a consistent enough pressure curve to reliably get bullets out of the barrel, which is potentially a dangerous situation.