At the 2017 SHOT Show, I had a chance to sit down with John Hollister, a suppressor guru who now works for SIG Sauer in it suppressor division. The subject was loading subsonic ammunition, both the factory ammo you can buy, and the ammunition you may be loading on your own.
Sweeney: John, what is the velocity target that works best for subsonic ammo?
Hollister: The problem factories have, and reloaders have, is how fast? Velocity is what makes bullets work, and you want as much as possible, but not too much or it goes supersonic, which noise a silencer can’t decrease. We all know what the speed of sound is, but what is the barrel length you’ll be using? If you or the factory loads ammunition to be subsonic, in a 9-inch barreled rifle, for example, how much extra velocity does that load get you out of a 16-inch barrel?
I’ve seen factory ammunition that came too close to the limit, and would have a round or three out of a box go supersonic. And a load that just stays subsonic in that 9-inch carbine, will go supersonic almost every time out of a 16-inch carbine.
In handgun ammunition, it is a lot easier. If it is subsonic in a 3-inch barrel, it is going to be subsonic out of a 5-inch barrel. But, as I said, put that same ammunition into a much longer barrel, and you might have problems. If you are loading your own, you will have to test to be sure.
This isn’t always an easy problem to solve. After all, velocity is what creates expansion, and you want as much velocity as you can, for terminal effectiveness. But no matter how much you want velocity, the speed of sound is not going to adjust to your desires.
Does SIG look at powders with an eye towards handling the barrel-length problem?
Yes, we carefully select powders with the intention to create the cleanest-burning load we can. There’s not much advantage in making a quiet load, but one that loads up your silencer in short order. At the same time, we try to make the load balanced. That is, as much velocity as we can get in a handgun, and stay subsonic, and still not go supersonic in a longer barrel. A lot of end users have both a pistol and an SBR (short-barreled rifle. Ed.) or a carbine, and they want their subsonic ammunition to be subsonic in all of those.
We look closely at all the powders available, and select the best one for a given caliber and bullet weight, not just in subsonics,