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Yosemite Steve · February 16, 2018, 11:36 PM

I have the Caldwell Precision model. It runs on a 9 volt battery.
I have tested it against a magnetospeed and mine reads 11 fps slow +or- 3 at 40F. I loaded up some rounds for my 10mm that have an average SD of 15 fps. At 50F outside I shot my rounds which were 70F as well as the gun at 1046 fps - SD was 17. That battery was about an hour old. At 10F outside I shot my rounds and gun at 70F (inside my truck temp) and got 1055 fps SD with a brand new warm battery from my truck. Today the same loads on an almost dead battery at 30F shot 1026 FPS - (SD was 24) with both the ammo and the gun at 30F.

I hope that helps. I think the cold ammo was the difference.
6.5 grains of Unique behind a 165 grain TMJ.

Also, as your ammo sat and cooled off it should have had an effect but I could not say how much. You could look up the temperature sensitivities for your powder.

February 16, 2018, 11:36 PM	#38
Yosemite Steve Senior Member Join Date: December 27, 2017 Posts: 460	I have the Caldwell Precision model. It runs on a 9 volt battery. I have tested it against a magnetospeed and mine reads 11 fps slow +or- 3 at 40F. I loaded up some rounds for my 10mm that have an average SD of 15 fps. At 50F outside I shot my rounds which were 70F as well as the gun at 1046 fps - SD was 17. That battery was about an hour old. At 10F outside I shot my rounds and gun at 70F (inside my truck temp) and got 1055 fps SD with a brand new warm battery from my truck. Today the same loads on an almost dead battery at 30F shot 1026 FPS - (SD was 24) with both the ammo and the gun at 30F. I hope that helps. I think the cold ammo was the difference. 6.5 grains of Unique behind a 165 grain TMJ. Also, as your ammo sat and cooled off it should have had an effect but I could not say how much. You could look up the temperature sensitivities for your powder.