Most of my silenced shots are from 22LR. Up to 1000fps it's noiseless, whereas 1050-1065fps gives an annoying "ripping noise" from bullet flight.

Of course this is nothing when compared to flight noise at or above the speed of sound. And it's less pronounced in bigger calibers. The extra 50fps is just not worth it for me.

But in what ambient temperature? The colder it gets to 32 F or zero centigrade the closer the speed of sound is to 1080fps.

At 0C the speed of sound in dry air is 1087.3 ft/sec. There is very close to a 2 ft/sec change in the speed of sound for each 1 degree C change in temperature. That simple rule works over the temperature range humans can tolerate. In my opinion for low bullet noise and optimum subsonic bullet stability muzzle velocity should be between 100 and 150 fps slower than the speed of sound. That does depend some on bullet shape but not a lot. I live in Arizona at a mile elevation and load for 1000 fps for 300 Whisper and heavier subsonics . Here there is low air low air density and temperatures from -20C to +40C. Speed of sound from 1040 to 1170 fps.

Rikky Lee, I notice the "ripping noise" year around. Basically sea level, temperatures maybe 0 to 70 Fahrenheit (around -20 to +20 Celsius). Fortunately also muzzle velocities are a bit lower in wintertime.

My biggest annoyance is that I've not found slow enough and cheap enough training ammo for 22LR. I just looked at my notes and the ammo I'm currently using (Eley Std) was averaging 1040fps in +20C/70F. CCI Std is pushing 1080+ fps. Other std vel are between them.

The difference from RWS subsonic (975fps) to Eley is significant but still tolerable. CCI I use only in pistol. RWS is damn expensive. I ought to gather some different ammo and have a chronograph session with my new Anshcutz full-size trainer (old bolt action biathlon rifle).

+1 on JBM

I took a readout of my .308 to my first Sniper Match and made 6/10 hits at 550yards off those charts alone, never having shot the gun past 100 yards before the match. Windage took the other 4 rounds off target. Was a life saver that day! I've since compared real world data to it and confirmed that it is dang close.

If you have an iPhone check out "Ballistic" as it uses the same formulas.

I also noticed that some companies only list a single BC for a bullet and that is usually based on a certain velocity that is probally alot higher than subsonic.

Sierra lists the different BCs as the velocity changes.

http://www.sierrabullets.com/bullets...ient-rifle.pdf

BCs get you in the park, the only data worth anything is that data logbook you keep. BTW I have a free one on my website that is very nice. :)
http://www.oregonshooter.com/index.p...rifle_logbook/