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https://en.wikipedia.org/wiki/Subsonic_ammunition

In dry air at 68 degrees Farenheit, the speed of sound = 1,126 fps (feet per second).

I have heard the term "subsonic ammunition" bandied about, but I didn't really know
what the deal was.

The above link is to educate others who didn't know about it.

.45 ACP in general would be subsonic, while other calibers are specifically engineered
to be subsonic by using a heavier bullet.

Feel free to comment friends.

SIA

Adding to that, I have found that the temperature of the loaded cartridge makes a huge difference when you are trying to load just below subsonic velocities . I believe I read somewhere that each temperature point increase is worth 1.5 fps in increased velocity. I have found that to be the case recently with some loads I had that I was using in conjunction with a suppressor, they were cracking when left on my reloading bench ( 90 + degrees in garage) for a few hours, those I took straight from the 70 degree house were not. I have yet to chronograph the difference though.

Weg wrote:Adding to that, I have found that the temperature of the loaded cartridge makes a huge difference when you are trying to load just below subsonic velocities . I believe I read somewhere that each temperature point increase is worth 1.5 fps in increased velocity. I have found that to be the case recently with some loads I had that I was using in conjunction with a suppressor, they were cracking when left on my reloading bench ( 90 + degrees in garage) for a few hours, those I took straight from the 70 degree house were not. I have yet to chronograph the difference though.

When you have some more time, please do so. I think the results would be very interesting.

I will add that, through a suppressor, there is a remarkable difference between the decibels of supersonic and subsonic loads. For example........

My 5.56 carbine, shooting supersonic ammo (i.e. M193, M855, etc.) unsuppressed, is plenty loud.

Suppressed with the same ammo, it is quite a bit quieter, but not what I would call hearing safe for repeated exposure.

Suppressed with subsonic 77 grain OTM ammo, it is hearing safe without earpro, and not any louder than someone clapping their hands.

Ditto the differences between shooting supersonic .300 Blackout unsuppressed and suppressed, and subsonic .300 Blackout suppressed.

The reason is that supersonic bullets carry with them the crack of a mini sonic boom. When you suppress a supersonic bullet, you virtually eliminate the muzzle blast, but you still have the supersonic crack of the bullet. With a subsonic bullet suppressed, there is no crack of the bullet's passage through the air, and all you are left with is the residual muzzle blast, which has been greatly reduced to the point of becoming a diffuse sound, which is difficult to locate at its source if you're on the receiving end.

You should also familiarize your self with the term "transonic" which refers to a range of velocities that are below, at, and above the speed of sound, typically accepted as +/- 20%.

For precision rifle, "long range" (shooting) is best defined as the distance at which the round becomes transonic (and therefore its behavior is far less predictable). When a bullet flies through the transonic region, the aerodynamics change. Transonic regionshockwaves shift from the tip of the bullet backward to the tail as the bullet approaches and then crosses the sound barrier at Mach 1.

In terms of ballistics and accuracy, the center of pressure shifts relative to the bullet's center of gravity, and this can cause instability. The result can then be the invalidation of the trajectory predictions made by ballistic software, and if there is an increase in wobble it can make the bullet tumble.