You just need a chart that shows speed of sound at different temps and compare that to your rated MV, recognizing that other factors are in play (elevation, for example).

Nice pictures here... but you'll have to convert metric to imperial.

https://www.nde-ed.org/EducationResources/HighSchool/Sound/tempandspeed.htm

Or you can let these folks do the math:

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

.

 

I was just discussing this very subject earlier today and tonight in THIS thread. You may find your answers there.

This Speed of Sound Calculator and it's page will shed light on your question as well as give a useful calculator to allow you to know the speed of sound at various temps.

Plug in your temp and it'll give you the speed of sound in various units including feet per second. If your ammo exceeds the speed of sound at the temp you're shooting it at, you get a sonic crack. Most ammo probably won't hit the manufacturer's published velocities, but if it's in the neighborhood there's a chance that some rounds will actually hit what they claim. About the coldest I'm likely to do much shooting is in the 40's. As a frame of reference, at 45 degrees, the speed of sound threshold is right at 1100fps. So, I tend to use 1100fps as my "magic number" to insure that my ammo will stay subsonic year round for me, in anything that I'll be using it in. Barrels of 4.5" or less will even keep most HV ammo subsonic in my experience. Whereas, in my rifles, some ammo that remains subsonic in the summer can start cracking in cooler weather.

 

Thanks Sophia, Poser. :bthumb: Looks like the hunt for even slower subs will commence.

 

ETA~ I've been getting intermittent sonic cracks from my 1050-1075 fps subs @ 15-20˚.....not good for clandestine termination of pests @ my locale.

 

Those temps put you in the 1070fps range as the speed of sound. With ammo that's listed as being that close in velocity it's more likely that some of the rounds will be a little "fast" and be enough to crack. You may want to check how the CCI Suppressors or the AE equivalent shoot in your guns. They are both 45gr bullets listed at 970 FPS so should remain subsonic down to -50*. At least theoretically...

From personal experience here in Colorado, Remington Cbees don't crack even below zero. My guess cci quiets also, will have to test. Happy hunting.

CBees are listed at 740fps. I can't imagine that they would ever be close to the speed of sound regardless of the temperature. With a listed velocity of 710fps, I'd say that the same would be true of the CCI Quiets. I haven't tested either since most of my rimfires are autos, save for one revolver, and one pump action rifle. I'll have a bolt action by this weekend though, so that'll open up more possibilities for experimenting, so I may play with the Quiets soon, just for kicks. But, honestly, with my Dead Air Mask on a bolt action, I see little need for anything other than subsonic LR.

 

From personal experience here in Colorado, Remington Cbees don't crack even below zero. My guess cci quiets also, will have to test. Happy hunting.

 

I had a number of rounds from a lot of Wolf MT go supersonic on me a few years back. As I recall, it was foggy and cold...so here's the rub: only some of them went subsonic under identical conditions. Good information presented here, but I doubt you'll find the exact answer to your questions, given the variability within any given lot of ammunition, and since measuring the velocity and atmospheric conditions accurately enough to determine the precise subsonic point is problematic. In other words, you'll always have the possibility of one cracking on you if it's close. The only answer is to use ammunition that is comfortably under the threshold, and there probably aren't many good choices there, without going to the above-mentioned lighter-bullet CBs or CCI Quiets, etc.

TBR

 

I agree. The calculator I linked to above is an accurate predictor of the threshold, but with the variability of ammo, if you're close to that threshold, there's a good chance that you may have some rounds go supersonic. Of course, the closer you are the higher the probability. And of course, the colder the conditions, the harder it is to find suitable ammunition. Luckily for me, I'm a wimp when it comes to cold, so I'm not likely to be out in the backyard plinking if it gets below 40* which puts me at 1095fps as my threshold. And honestly, I'm more likely to be out back shooting when it's 60* and above. But even at my coldest tolerance, I feel pretty confident that the Suppressor ammo that I mentioned above, that's rated at 970, would be unlikely to be over 100fps faster than their manufacturer claims them to be.

Of course, this is all based on "theory" and there's nothing better than actual experimentation to prove or disprove a theory. Being that I've bought/built 5 .22LR suppressor hosts in the last few months, I'm hoping to be doing some experimentin' myself this winter.

 

Don't forget

that even if a projectile is moving at subsonic speeds, if it has a blunt nose it can still generate a weak shock wave while moving at only M 0.9-ish.

Transonic speed (where shock waves begin to form) starts at M 0.92 to 0.95 for many jetliners. Is your 40 grain .22 bullet as pointy, streamlined, and sexy as the nose of a jet airliner?

 

The only answer is to use ammunition that is comfortably under the threshold, and there probably aren't many good choices there, without going to the above-mentioned lighter-bullet CBs or CCI Quiets, etc.

TBR

Of course, he could just use a gun with a shorter barrel for cold weather pest termination.

 

That was one of my solutions...

Not that I actually have "pests", but still... It's fun!

And keeps everything subsonic at "normal" temps.

 

Don't forget that your muzzle velocity drops as temp drops. Biathlon ammo is higher velocity because of this. Guess ya need a chart showing loss of speed per degree of temp loss.

 

I shot a sport called .22 Benchrest Silhouette which is shot from 65 to 200 meters. I know from both experience and my ballistic calculator that at 200 meters, ever 10 degree change in temp is worth one 1/8 minute click at 200 meters. The may not sound like a lot but when you have a sight in period early in the morning when the temp is 50 degrees and by the time you shoot for record the temp has climbed to 80 degrees it can make a difference. Yes where I live those kinds of temp changes from morning to noon can and do happen.

 

I just saw a video today of the fella who broke the record on distance for shooting. One of the things mentioned was that the colder air meant denser air. I would think denser air would cause the bullet in flight to have more drag.

However I'm wondering if the colder temp is effecting your barrel possibly influencing the bullet.

 

I like this article https://bisonballistics.com/articles/pressure-temperature-and-himidity-for-ballistics-calculators

I keep a copy of the link to it on my tablet's homescreen in a folder called "Ballistics". Useful to re-read every now and again to remind myself of the effects of pressure, temperature, humidity on air density.
I keep getting the effects of humidity reversed

 

Density altitude is what we use as pilots the most as it combines several of the others & IMHO if you do it by hand would be more important & eaier to use.

 

Yeah, you're right. My info is in my notebook in the shooting box in the shop and I was too lazy to check. But to my defense, I never have to look at it because the Humidity doesn't change much here in the summer. Sorry. But now that you brought it up, I wonder how much that affects drop.

Just for giggles, if I shoot at 5500 feet and the drop is 66.55 inches, I checked and the drop at 500 feet is 69.19 at the same temp. The is why I don't do sight ins at 7000 feet where I live but shoot at 5500 feet.

I'v been working with a friend who shoots a .308 We check the actual vertical adjustments at 5500 feet in 70 degree weather against the ballistic calculator but since he hunts at 10000 feet in 30 degree weather we have to adjust his scope settings since he can't sight in under those conditions. Isn't ballistics fun.

 

Temperature and altitude have a much greater effect on ballistics. From what I've read in the past, the most humidity can affect the speed of a bullet is a max of 1.5%.

 

Try using this one: http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/souspe.html

 

I think You are exactly onto the issue, the more dense medium is what allows the sound barrier to be broken by the slower moving projectile, I think it is because it compresses more readily to create the shock wave, but would need a more knowledgeable person to confirm or correct me there.