#Supersonic

So I have been going down a slow-motion rabbit hole. I recently posted about the Slow Mo Guys’ recent video where they filmed eggs being shot by 9mm bullets and filmed them at various frame rates up to 1 million frames per second. Well, Destin of Smarter Every Day has a video he made back in 2018 looking at shockwave shadows coming off supersonic and subsonic bullets.

When we last left you, the discussion of choosing either subsonic or supersonic ammo for your 300BLK defensive weapon was in a full-on firefight. Some of you stated that you would pick heavier and quieter rounds to preserve situational awareness and communication abilities. Others chose faster and lighter rounds because “it’s a rifle, not a pistol”. And a small percentage of you claimed that using a 300BLK AR15 in a life or death situation was nothing more than a mall ninja’s wet dream. An argument for another day…

As a follow up to last week’s Silencer Saturday where I professed my allegiance to the god that is 300 Blackout, I thought it might be a good idea to discuss my conversion in a little more detail. As I stated, my initial reaction came after comparing an MP5SD alongside a Sig Sauer Rattler with a proper decibel meter on loan from Allen Engineering. In the comparison, the Rattler shooting 220gr subsonic ammunition from Sig Sauer noticeably outperformed the MP5SD shooting 124gr JHP ammunition both in dB readings and old fashioned “that sounds loud” testing. Which is part of the reason I now love 300 Blackout.

Previously, we compared the Russian 9x39mm subsonic sniper round to its Western counterparts, including the .300 AAC Blackout and the .45 ACP. As it stands now, the 9x39mm is a subsonic round only – no supersonic loads exist for it currently. But… What if they did?

Manufacturer SIG Sauer brought along their brand new MCX Rattler ultra compact 5.56mm and .300 Blackout assault rifle/carbine to the 2017 Association of the United States Army annual meeting. The Rattler is an ambitious design intended to bring a reliable extremely short barreled AR-type rifle to the military and civilian market. Historically, designing very short barreled gas operated rifles that function well has been a serious challenge, so the Rattler’s designers had a tall order to fill.

SIG Sauer has announced a new addition to its nascent ammunition line: Supersonic .300 Blackout. Loaded with 125gr Sierra MatchKing projectiles, this load rounds out the SIG-branded .300 Blackout for their MCX rifle. From the press release:

Jeremy S. of Guns & Gear YouTube channel created an interesting little video of shooting supersonic and subsonic ammunition out of handguns and the CZ Scorpion Evo 3. While the results are predictable, its incredible to hear the shots side-by-side and shooting on steel.

The flight of a rifle bullet may seem to be a simple thing – it flies through the air at high speeds, steadily losing velocity and energy until it either impacts the dirt or simply falls out of the sky. In fact, though, there is a lot of complex fluid dynamics to absorb to fully understand the flight of a bullet through the air, especially as that bullet drops below Mach 1.3 (about 1,450 ft/s) and encounters the transonic flight regime. To help us understand what happens better, we’ll turn to an instructional video from the 1950s from Shell Oil; while it covers the flight of then-high-performance aircraft, not bullets, the basic principles still remain the same. I highly recommend my readers watch the video first, before reading my discussion of it: