Like most ammunition comparisons, there are a lot of misunderstandings of the differences between the 300 Whisper vs 300 Blackout. Similar to our articles over the differences of .223 vs 5.56 and .308 vs 7.62, we thought it would be helpful to explain each round, what the difference between the two are, and whether you can chamber them interchangeably.
Developed and pioneered by J.D. Jones of SSK Industries in 1992, the .300 Whisper was originally developed from its parent case the .221 Fireball. It can be loaded to subsonic or supersonic, with the subsonic being ideal for suppressed shooting. The .300 Whisper is a wildcat cartridge meaning there is no set, published standard like a Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) standardized round has. The absence of this set standard means it can be loaded hotter than normal, and is often used for handloading.
.300 AAC Blackout
Developed by the Advanced Armament Corporation (AAC) in 2009 and inspired by the .300 Whisper, the 300 Blackout (300 BLK) is a SAAMI standardized round. This means that there are set specifications and dimensions used by all ammunition manufacturers when making the 300 BLK, for consistency purposes. Offering better performance than the standard 5.56 NATO, the 300 BLK is available in high velocity rounds that match that of the 7.62×39 ballistics. The thought was to make a commercialized .300 Whisper while fixing the problems of the wildcat .300 Whisper. Interestingly enough, the “300 Blackout” would have never been developed under a different name if SAAMI had accepted trademarked cartridge names.
In most respects, the 300 BLK is identical to the .300 Whisper. One of the slight differences that has been found is the 300 BLK has a slightly longer neck on the cartridge (similar to the difference between .223 and 5.56). Also, since there are no set specifications for the .300 Whisper, the chamber pressures of a particular loaded round may be too hot to chamber in a 300 BLK chamber. For this reason, it is important to be sure that the .300 Whisper is loaded properly, and does not exceed the recommended maximum load for a 300 BLK rifle. Most of the large manufacturers of the .300 Whisper have tested it in a 300 BLK rifle and have approved its ability to safely shoot. The problem comes from other non sanctioned “wild” cartridge versions of the 300-221 that have incorrectly been called .300 Whisper. So yes you can fire .300 Whisper out of a 300 BLK firearm if the ammo is commercially loaded, or loaded less than the maximum load for a 300 BLK. If you have any doubts contact the ammunition manufacturer or seek advice from your local gunsmith.
While it is completely acceptable to chamber and fire .300 Whisper in 300 BLK, there has been a lot of controversy regarding if you can fire 300 BLK in a .300 Whisper rifle. According to Robert Silvers from AAC, “If you shoot .300 BLK ammo in chambers that have a shorter or tighter throat, pressures will go up– perhaps above SAAMI maximums.” So to say it isn’t possible would be a lie, but you need to be more cautious when chambering 300 BLK in a .300 Whisper rifle.
So as you can see there aren’t that many differences between the 300 Whisper vs 300 Blackout, but it makes a huge difference that the 300 BLK is SAMMI standardized, and requires little change to be fired from a 5.56 AR 15 platform other than a barrel swap. To learn more about the 300 Blackout Click Here.