Subsonic loads?

[RMc]

With all the interest in subsonic rounds, just how slow, (or fast), is that?

"The speed of sound is dependent on the density of the air...and the density of the air is dependent on the temperature of the air."

https://www.weather.gov/epz/wxcalc_speedofsound

[jdfoxinc]

Here at 5280' I try to stay below 950 ft/sec. That covers most conditions normal here.

[Petrol & Powder]

1087 fps at 32 F and dry air at sea level +/- a bit depending on atmospheric pressure and humidity.

If you stay below 1070fps you will generally not break the sound barrier in temps above 32F.

[RMc]

So, cold air is dense air and it applies the brakes to the sound barrier - interesting.

So what other performance aspect of shotgunning would air temperature have an effect on? Why?

[Cap'n Morgan]

Normally the speed of sound is around 1100 fps, but for best noise reduction the speed should not exceed 1000 fps:

https://i.imgur.com/nBv1ntG.gif

[RMc]

So what other performance aspect of shotgunning would air temperature have an effect on? Why?

:coffee:

[Cap'n Morgan]

So what other performance aspect of shotgunning would air temperature have an effect on? Why?

You mentioned it yourself "The speed of sound is dependent on the density of the air...and the density of the air is dependent on the temperature of the air."

Colder air = higher air density = more air resistance = slower pellets.

Also, all smokeless powders are influenced by temperature. Normally the variance is insignificant, but I have tried several factory loaded cartridges which would produce partial "bloopers" when the temperature dropped below freezing.

[Petrol & Powder]

Like most things in the firearms world, there is some compromise involved.

For shotgun sports the compromise can be pellet deformation. The faster you launch the pellets, the greater the chance you will deform a large number of them (make them less spherical). Deformed pellets will open up the pattern sooner and they will also loss velocity at a faster rate. Deformation can be reduced with harder shot, good wad design, buffers and back bored barrels but there are diminishing returns to those methods.
Additionally, even if you start the pellets at a higher velocity, they lose velocity at a faster rate when travelling at higher speeds. In other words, the loss of velocity isn't linear.

So while there are some gains to be had from launching the shot column at a higher velocity (like the ability to cover the distance to the target in a shorter time making lead estimation less critical), some of those gains are offset by larger patterns and other issues.

Skeet shooters deal with short ranges and high speed crossing shots; they welcome patterns that open up quickly.
Trap shooters know that a tighter pattern will get the job done. They want pellets that remain round and patterns that stay dense. Speed is not as important to them.

Compromises cannot be eliminated and we must pick the traits that we want the most. When dealing with shotgun pellets, transonic performance of the pellets isn't nearly as critical as the shape of the pellet. A sphere isn't a very aerodynamically efficient shape to start with but a sphere is FAR better than some oblong chunk of lead with random flats. If I need a pattern that remains dense and compact at long distances, I may be better off starting with a slightly slower speed and not damaging those little spheres.

[RMc]

You mentioned it yourself "The speed of sound is dependent on the density of the air...and the density of the air is dependent on the temperature of the air."

Colder air = higher air density = more air resistance = slower pellets.

Also, all smokeless powders are influenced by temperature. Normally the variance is insignificant, but I have tried several factory loaded cartridges which would produce partial "bloopers" when the temperature dropped below freezing.

Yes, retained shot velocity is lower in cold temperatures.

However, there is another aspect overlooked by most shotgunners. To paraphrase your response:

Colder air = higher air density = more air resistance = lower pattern density.

Velocity and air density are the twin engines* of pattern spread. This becomes most pronounced at longer shotgun ranges; but is indeed evident when patterns made made at normal ranges in the heat of summer are compared with those made in cold weather, (assuming the same load/barrel/choke).

*Deformed pellets also lower pattern density.