Subsonic Speed and Temperature

[breezernate]

I noticed last summer I could fire certain target ammo from my rifle with a suppressor and have a very quiet setup with no sonic crack. I then noticed as the weather got cooler with the same ammo, it started to crack and make lots of noise. I forgot the muzzle velocity 1100-1150 fps?

I suppose it is best to stay with a round around 1050 fps?

Remington Subsonic HP works well in my rifle...1050 fps? CCI target pistol work great. RWS cost too much and didn't shoot any better.

Nate

 

[kombayotch]

Re: Subsonic Speed and Temperature

The best target ammo I have found for cold weather shooting is Eley Match Pistol. It runs at 1000 fps. out of my Quad and is nearly as accurate as Eley Match at 200 yards.

I tested it again the other day when the weather was hovering around 0 deg. F. No sonic crack at all.

 

[TimK]

Re: Subsonic Speed and Temperature

I tested Eley yellow box over the chrono a while back. I put some in the freezer (about 5°F), and the control was at room temp. I could see no difference in velocity between warm and cold.

 

[kombayotch]

Re: Subsonic Speed and Temperature

It isn't about the velocity of the ammo changing with temperature, the speed of sound does. A lot of ammo that is subsonic in the summer is not in the winter even if its velocity has stayed the same.

 

[SPAK]

Re: Subsonic Speed and Temperature

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kombayotch</div><div class="ubbcode-body">It isn't about the velocity of the ammo changing with temperature, the speed of sound does. A lot of ammo that is subsonic in the summer is not in the winter even if its velocity has stayed the same. </div></div>

Kombayotch is right. you can do a quick google search on google for a speed of sound calculator. Input a temperature, and then input a lower temperature and see how the speed of sound increases or decreases.

My subsonic .30-06 loads in the summer running 1090 fps make sonic crack at 0 deg here in the winter.

 

[Cheech]

Re: Subsonic Speed and Temperature

http://convertalot.com/speed_sound_calculator.html

 

[Lindy]

Re: Subsonic Speed and Temperature

The speed of sound is a function of temperature - not air density.

http://en.wikipedia.org/wiki/Speed_of_sound

Don't neglect the fact that muzzle velocity is also a function of temperature.

 

[breezernate]

Re: Subsonic Speed and Temperature

I would think humidity would also affect it. I think density is a part of that, so doesn't humidity affect air density?

Nate

 

[Spazz.]

Re: Subsonic Speed and Temperature

The air gets more dense as the temperature goes down. The air gets less dense as the humidity rises. The speed that sound travels gets slower as air gets more dense.

If it's cold, the speed of sound is decreased. Therefore, if the speed of sound is lower than "normal," a subsonic bullet will become supersonic if it's moving faster than sound. If there is more humidity, the speed of sound increases. This can cause a normally supersonic bullet to travel at subsonic speeds, getting rid of the destabilization that comes from the supersonic-subsonic transition.

If you look at the basic temperature and don't factor in humidity, altitude, or any other variables, you're looking at a difference in sound speeds like this:
100° F - 1160 fps
70° F - 1130 fps
50° F - 1110 fps
32° F - 1090 fps
0° F - 1050 fps
-10° F - 1040 fps
Any colder than that and this Kentucky boy thinks you're crazy for practicing rimfire shooting.

For "sane" or "normal" (like any of us fit those criteria) shooting conditions, 1050 fps will keep you subsonic. Someone else feel free to correct me if I'm wrong, but 1240 fps should keep you supersonic out to around 100 yards.

 

[Dollar Bill]

Re: Subsonic Speed and Temperature

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BigNate</div><div class="ubbcode-body">I would think humidity would also affect it. I think density is a part of that, so doesn't humidity affect air density?
Nate</div></div>
High humidity makes the air less dense. It's counter-intuitive, but true.
The speed of sound is based on temp. If my memory serves me, the temp decreases with altitue up to about 60K ft. At that point, temp stabilizes up to about 80K ft, so the speed of sound stays constant, even though atmospheric pressure continues to decrease. At 80K ft, the air (what little there is) actually starts to increase in temp so the speed of sound increases.

 

[TimK]

Re: Subsonic Speed and Temperature

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kombayotch</div><div class="ubbcode-body">It isn't about the velocity of the ammo changing with temperature, the speed of sound does. A lot of ammo that is subsonic in the summer is not in the winter even if its velocity has stayed the same. </div></div>

Yeah, I get it. Thought the OP might also want to know that the powder isn't temp sensitive.