At near 6000 ft elevation you may well be running up against the transonic range. The speed of sound is lower at higher elevation. Get your velocities down below 950 fps and you should know for sure.

thanks for the help. always appreciated.
NT

The speed of sound in the air is inversely proportional to temperature and not related to altitude (except that at higher altitudes is is usually colder). The speed of sound is the same at 78 degrees at sea level or 78 degrees at 5000 feet. The basic rule of thumb is the colder it is the slower the speed of sound, the easier it is to get noisy (transonic) lead downrange.

OK, you ABSOLUTELY HAVE TO TRUST YOUR PARTNER ON THIS...stand at the 100 yard berm and have him shoot over the 100 yard berm into the 200 yard berm. You will understand just how quiet the Whisper is at 1000 FPS with a suppressor, and just how hard that damn round hits. The impact into soft dirt at 200 yards (100 yards away from you) will be much (maybe 3 or 4 times) louder than the sound at the firing point...ask me how I know.

Kevin

PS: I need to take some video of this and post it here. It's a real eye opener. Imagine someone whistling, without the tone, making just the sound of the air coming out. This is what it sounds like as the bullet goes by. Incredible.

Hopefully going to get some time to get out this weekend and tinker with some new loads. I'll let you all know if I get any better results.
NT

A Couple Handy Calculators For SOS. And Don't Overlook IMR 4759. I have been working with it for several years with the 7.5X55 Swiss ie. read .30 Cal. But you have to work this up or down for your particular application.

Links To SOS Calculators:

http://www.sengpielaudio.com/calculator-speedsound.htm
http://www.srh.noaa.gov/epz/?n=wxcalc_speedofsound

mmmmm K31 7.5x55. The things I've done with that gun.....:wink:

You just have to love an Old Mil Weapon that will shoot MOA with a 160 Gr. Cast GC Bullet atop 19.0 Gr IMR 4759. And has the recoil of a .22 Hornet.:smile:

John,

Thanks for the links. I was just wondering how much the speed of sound would change with temperature. I am getting ready to send our 50 THUMPER up to Ohio for a show and tell and want to make sure I get the load right.