Cold weather chronying?

gkosztrub

gkosztrub

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Hey guys,

I am trying to work up a new load for my CZ SP01 for IPSC.
Win case & primer, 3gr of TiteGroup powder, and 138gr RN CMJ from Frontier.

It was -12C on Sunday when I Chronied the load. It averaged at 870fps.
Does the cold have any effect on the speed? If I were to chrony the same load indoors, would I get a different result (faster, slower)?

Thanks
 
I understand that most loads will be slower in the cold than if it was warm out. The cold reduces the pressure in the case. However the difference is varied from 60-100fps for the average load for a rifle maybe a little more. Anyone is free to correct me if I'm wrong on the fps. ;)

Good luck!
 
Cold air is denser, cold powder will burn with less pressure, but the difference will be trivial, in the 10 ft to your chrony
 
depends on the powder. some powders are more tempature sensitive then others. there use to be one out there that got faster as it got colder but i can't for the life of me remember which one it was. i would suggest you work a load at a power factor of 10 over (about 70 FPS) what you want till you get a chance to do some temarture comaprission.
 
To compare fire a mag over the chrony when the gun/ammo is toasty warm from the car and then when it gets down to ambient temp try again. I don't think you'll find much diffrence in FPS between -12C and and a warm spring evening.
 
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Chronys' use light to ascertain velocity. When the bullets cross the screen they cause a measureable anomaly between the entrance and exit screen. When there isn't enough overhead light on the screens, velocities will either be recorded slower or vary.
Chrony's aren't really to give super accurate velocity readings, (though they usually do an excellent job of it when compared to wire screen testing), but are intended to show consistency of velocity for a load or batch of commercial ammo. bearhunter
 
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