After my field testing, I concluded there is very little difference, if any, between the .300 Whisper and .300 AAC Blackout. So if they’re virtually identical for practical purposes, how, exactly, are they different? Silvers told me: “I have never seen an SSK .300 Whisper drawing—it is proprietary to SSK, so it is hard to say how it is different. We focused .300 BLK on normal full-power ammo rather than subsonic-designed ammo, which is optimal for existing U.S.G.I. magazines, and developed rifles which can shoot all types of ammo without requiring an adjustable gas block.”

“The development process was to take the Remington .221 Fireball drawing, opened it to .30 cal., keep the headspace the same, move the headspace datum point to not be on a radius, and then picked a chamber neck diameter that would allow compatibility with most existing brass,” Silvers said. “We also picked a throat that would be long enough so that a Sierra 220-gr. MatchKing could be loaded to full magazine length of 2.260" and have 0.010" jump to the lands. The added benefit of this longer throat is to allow for higher velocities with normal ammo. Because this throat is longer than some of the wildcat chambers, pressure may go up if you shoot .300 BLK ammo in a wildcat chamber,” Silvers concluded.

Asked how they are different, Jones replied: “I don’t really know—the few [.300 BLK] cases I’ve seen appeared to me to be identical with the Whisper cases made by Hornady except for the headstamp. It is supposed to have a longer throat from what I read.”

So we’ve determined that there’s not a lot—if any difference between the two cartridges—so why the change of names?

When asked why AAC went with .300 AAC Blackout instead of .300 Whisper, Silver said “.300 Whisper is not SAAMI-approved and SAAMI will not accept trademarked cartridge names. Over the years, there have been many versions of taking a .221 Fireball or .223 case and making it .30 caliber. Several of them have similar, but not identical chambers. In order to assure ammunition and firearm and ammunition compatibility and interchangeability, an industry standard was needed. This required picking a final set of specifications, and submitting it for industry consideration. Also, if we did not pick a new name, then we would have had to make the round compatible with the tightest chamber ever called .300-.221, .300 Fireball or .300 Whisper—and that would have limited supersonic velocity in the same way that the tighter throat of .223 Rem. chambers cannot shoot as hot ammo as 5.56 mm chambers.”

Finally, I asked Jones and Silvers to sum up the .300 Whisper/.300 AAC Blackout differences as best they could in a final statement, to which Jones replied, “If it looks like a duck, talks like a duck, flies like a duck, walks like a duck, it is essentially a duck. At this point the SSK adjustable gas system is a huge advantage, and the S&W single port system works with all the Hornady ammo.” Silvers summed up with the “.300 AAC Blackout is the SAAMI standard and over 85 companies have announced their support by making products for it.”

The .300 Whisper was not the first .221 Fireball necked to .30 caliber, but it is well-thought-out, well-documented and the most popular. When Jones created the Whisper series of cartridges, he developed a genre that most definitely has legs. When it comes to the .300 AAC Blackout, Silvers and AAC have done things “by the book” and are well positioned with a SAAMI standardized cartridge.

Conclusion
Is there really that much difference between the .300 Whisper and the .300 Blackout? Given the fact that major manufacturers such as Hornady are building ammunition headstamped .300 Whisper and recommending it for use in either platform—in addition to producing reloading dies that are marked “300 Whisper/Blackout” and Smith & Wesson stamps the barrel of its M&P-15 Whisper barrels with: “300 Whisper/300 AAC Blackout” it is safe to say that differences are minimal. Through the years lots of great cartridges have gone by multiple names, i.e.,7x57 mm Mauser and .275 Rigby. Will the “Whisper” or “Blackout” names stick? Only time will tell. Either way, J.D. Jones developed the concept of a high-velocity/subsonic dual-role cartridge in 1992 and has done much through the years to perpetuate the concept. For any who doubt, it has all been well documented in industry reference books such as Cartridges Of The World and others. That said, there is new momentum behind this cartridge, whatever the world wants to call it.

Shooting Results