Subsonic Ammunition

300BKTGIF readers! It looks like we’ve made it through another week and look forward to a nice weekend. Weather here at the bat cave has been excellent and this weekend looks to be just dandy. BTW, Happy Mother’s Day to all of my mom readers. You deserve it but always bear in mind that motherhood is about the journey and not just the event.

This Friday’s shoot-the-shit topic is subsonic ammunition, but if you’d like to change the subject to how great Fox News’ Andrea Tantaros or Kimberly Guilfoyle would look in OCP thongs I’m up for that as well. As with all shoot-the-shits, you a free to make any unsupported statements or claims, use profanity, change subjects and insult anyone or anything.

Subsonic ammunition is ammunition that has been loaded to have a muzzle velocity of less than 1100 feet per second. It is generally used in conjunction with a suppressed weapon; however, as cool as subsonic ammo is it has a very specialized and limited use.

Throughout the year, I get several questions on the subject that revolve around effective range and projectile weight, so I’ll start by providing some background that’s important for you to have if you want to maximize the effectiveness of this type of ammunition. I’ll begin with air.

Air is very much like a fluid from a physics point of view. Have you ever been in a swimming pool and noticed that as you swim, or frolic, in the water you encounter pockets of colder and denser water? The same holds true for air. Sound propagation is influenced by these layers; a perfect example is sonar. Submarines are able to use these thermoclines to avoid detection. The sound  or ping emitted by a sonar transducer reacts differently as it encounters these layers. The same holds true for a projectile moving through the air. If a projectile moving faster than 1100 feet per second encounters an air mass where sound propagates at 960 feet per second you will hear a sonic crack, sounding very much like a firecracker. If a projectile passes through air that propagates sounds at  1000 feet per second, at 960 feet per second, you’ll hear nothing. So, air temperature and humidity influence the acoustic characteristics of a subsonic projectile along its flight path.

Another characteristic of subsonic ammunition is best understood by discussing kinetic energy. Kinetic energy is calculated using the following equation…

k=mv2/2

Longhand this is what the equation is saying. Kinetic energy “k” is equal to mass times velocity squared quantity divided by 2. What does all this mean?

Without actually crunching numbers we can simply evaluate the equation, which tells us that velocity has the greatest impact on kinetic energy for any given value of  mass. Why is that? Because velocity is raised to the power of two, or squared; therefore, if we reduce the velocity of a bullet we decrease its kinetic energy, and this is the reason subsonic ammunition will generally have a much heavier bullet. A more specific example follows.

A .308, for example, is normally loaded  to a muzzle velocity of 2600 fps. In order to make it subsonic, we decrease the load from 2600 fps to say 1000 fps and in the process greatly reducing its kinetic energy. To compensate for the loss in velocity, manufacturers will top it off with a 220 or 240 grain bullet instead of a 168 grain or 175 grain projectile. It still has a lower kinetic energy overall because mass has less of an impact on kinetic energy than velocity – mass is not raised to a power.

The heavier bullets when combined with the lower velocity means that as range to the target increases, more energy is dissipated faster, and for that reason subsonic ammunition has a very limited range. For rifle calibers, 250 yards is usually max. and claims of 900 yard shots with subsonic ammunition can be generally classified as bull shit.

Subsonic ammunition is ideally suited for use in handguns and bolt action rifles. This ammo will not cycle the action of a semiautomatic rifle reliably, if at all. However, in a bolt action rifle the only thing the shooter will hear is the sound of the hammer striking the firing pin.

To summarize, subsonic ammunition will exhibit the following properties.

  1. in flight acoustic signature will vary with atmospheric conditions. If the bullet velocity exceeds the sound propagation velocity along its flight path, you will hear a sonic crack similar to that of a firecracker. The best loads in my experience are 960 fps up to 1000 fps. When working with your loads be alert to chamber pressure limitations.
  2. Subsonic ammunition will not reliably cycle the action of a semiautomatic rifle; therefore, use should be limited to  pistols and bolt action rifles for best results. Using subsonic ammunition in carbines like the M4, SCAR, etc., means you’ll have to manually charge the weapon.
  3. Subsonic ammunition with its heavier bullets perform extremely well at ranges not exceeding 250 yards and 150 yards optimally. Forget 1000 yard shots with a subsonic load.

Have a great weekend everyone and Mother’s Day!

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