Ammo 101- WHAT IS SUBSONIC AMMUNITION? AND SHOOTING WITH SUPPRESSOR?

I have added another link to the blog on my website, Ammo 101. These are topics I discuss often from shooters and customers, along with suggestions from shooters like yourself. Keep the ideas and questions coming!

https://dallasreloads.com/ammo-101/

WHAT IS SUBSONIC AMMUNITION? AND SHOOTING WITH SUPPRESSOR?


With suppressors being very popular, I wanted to post some information about SUBSONIC ammo and the differences between subs and super sonic ammo, and shooting suppressed. SUBSONIC, in terms of ammo, simply means the bullet is going below the speed of sound. The speed of sound is about 1110 fps, depending on your exact environmental conditions. To allow for some variables in barrel lengths and such, my subsonic ammo runs about 1000-1060 fps. When a bullet is going below the speed of sound, there is no sonic “crack” and the bullet has a very quiet flight. When a bullet goes above the speed of sound (about 1110 fps), the bullet will now have a sonic “crack”, just like the end of a cowboy’s bull whip. (The reason why a whip has a “crack”, is because the end of the whip breaks the sound barrier). A SUBSONIC round will have no sonic crack. When shooting this SUBSONIC round suppressed, the suppressor will muffle the bang, and the round will be very quiet. (See “Energy of a SUBSONIC” round below).



Energy of a SUBSONIC

To make a SUBSONIC round, the ammo is loaded to a much lower pressure to keep the bullet below the speed of sound, about 1000-1060 fps. With these slower speeds, the energy of the round has been heavily reduced. Take a SUBSONIC 308 Winchester with a 180 grain bullet going about 1040 fps. This round has about 430 ft lbs of energy at the muzzle, and about 380 ft. lbs. of energy at 100 yards. In comparison, a 40 S&W handgun round pushes the same weight 180 grain bullet about the same speed of 1040 fps as a 308 SUBSONIC round does. So, this 308 Win SUBSONIC round has almost the same energy as a 40 cal round, but fired out of a rifle platform. So, keep this energy level in mind. Also, at these slower speeds, the bullet will not have any expansion. With a standard bullet, the bullet will often, what I call ice pick through your target. The bullet has no expansion and minimal hydrostatic shock. A full power super sonic 308 Win round will have about 6.5 times the energy of a typical SUBSONIC round. So, keep this in mind when hunting with a subsonic round.



SUPPRESSORS!!

A lot of shooters get a suppressor, and think that they now must shoot subsonic ammo. You can shoot any ammo you want that you would normally shoot, including full power super sonic ammo or subsonic ammo. Just keep in mind that when you add a suppressor you raise the pressure of the ammo you are shooting about ~3000-5000 psi. So if you are shooting a stiff load that’s near max pressure without a suppressor, adding the suppressor can easily increase your pressures to make it a warm or hot (i.e. unsafe) load.

Great info Chad.

Is this why the subsonic 300BO is so popular over making the 308 subsonic? You might as well have a smaller and lighter platform to achieve the same goal?

Yes! There's a couple big differences between the 2 rounds, even though they fire the exact same .308" diameter bullets. The 308 Win typically has a barrel twist of 1:12" to 1:10" twist. The blk out is spec'd for a 1:8", and some are 1:7" twist. The faster twist of the blk out will stabilize a longer bullet, meaning heavier. Therefore you can get more energy on target with the blk out. Also, the blk out was designed to cycle subsonic rounds in the more compact AR-15 platform. It does this by opening up the gas port on the barrel and allowing more gas (pressure) to come back to cycle the action. Most AR-10's in 308 Win have a gas port opening of about .08" and a 300 blk out has a gas port opening of ~.125". This allows much more gas and pressure to come back to the action when a subsonic 300 blk out round is fired for cycling.

So with them both being subs, you said the 308 doesn’t expand, how does the BO perform?

There are a few bullets that expand at sub velocities at least for the 30 calibers. Hornady is now offering one in factory ammo at least for the 300BO. See a post by Ccoker if his son using it from a suppressed TC contender on hogs.

If planning on hunting with subs I like handgun rounds as the bullets are already designed for lower velocity than about all rifle bullets and if using a 44 or larger a heavy large flat meplat bullet is very effective on game.

I have some subsonic .22 lR ammo that I use to shoot in my suppressed .22 10/22 and 77/22..

Thank you for taking the time to explain this. I have wondered how this worked with a suppressor.