It appears the ammunition would have problems breaking the sound barrier when the temperature drops below freezing.
It’s so close that temperature can be a factor in going supersonic.
Along with barrel length of course.
It appears the ammunition would have problems breaking the sound barrier when the temperature drops below freezing.
More importantly, air density, which atmospheric pressure, temperature, and humidity are factors. The speed of sound is affected by the density of the material it is traveling through. Best to simply use a Standard Atmosphere of 29.92 “Hg and 59°F, look up the speed of sound at sea level and your altitude and subtract 5%. Just forget tying your brain in knots figuring the true speed of sound.
Speed of sound is about 1,100 fps at sea level to 8,000 feet, and 1,000 fps above that for Standard Atmosphere.
Subsonic at 5% below Standard Atmosphere would be 1050 fps below 8,000 feet and 950 fps above 8,000.
I just remember subsonic is 1,000 fps, to keep it simple as I live in Florida. In Colorado at 6,000+ feet, where I used to live, I remembered it at 950 fps.