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Subsonic And Other Misunderstood Buzzwords.

Recently somebody asked me for data that would produce a load that was subsonic in his .45 ACP pistol. He has doubtless fallen victim to some clever marketing. Several years ago Winchester began labeling some of their ammo that way and now it seems as if almost everyone is doing it.

Subsonic simply means that the projectile is traveling below the speed of sound. I'd bet that some shooters think it's important. It surely used to be a problem for airplanes, but bullets fired from rifles -- and a very few handguns -- exceed it with impunity.

The actual speed of sound varies with a whole bunch of factors such as altitude, temperature and other barometric measurements, but to keep it simple we can say that it is about 1,100 fps at sea level, (As altitude increases, the speed goes down.)

Is there something relevant to shooters here? Bullets that exceed the speed of sound announce their passage with a distinct little sonic boom, but unless you're downrange from the gun, that noise is usually obscured by the report from the firing.

Subsonic ammunition is often used in weapons equipped with suppressors to prevent the sound of the bullet from giving away the gun's location, but other than that there isn't any evidence to suggest that being subsonic or supersonic is an advantage by itself.

In fact, there's one troubling aspect that occurs in the instant when a supersonic bullet slows down and becomes subsonic. There is some evidence that the turbulence created by this "transonic" transition can have a negative impact on accuracy.

For most centerfire rifles, this doesn't happen until the bullet has gone a long distance but, with some rimfires it can happen in less than 100 yards. Opinions are mixed as to how big a problem this is -- or whether it is a problem at all -- but logic would suggest that it could be a significant factor if tackdriving accuracy is a concern. Rifle shooters would be well advised to at least consider it; I doubt that it would amount to a hill of beans for the majority of handguns.
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Publication:Guns Magazine
Article Type:Brief Article
Geographic Code:1USA
Date:May 1, 2000
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