Re: Cold weather velocity
Greyfox is right.
I'm up in Alberta, Canada and shoot in temps ranging from say -15F to also high 80's during summer months.. in fact just this past saturday was out doing some shooting, about -5F (-20C) using the Hodgdon powders.. my Muzzle velocity changes literally nothing, but the rate in which the air-density slows the bullet downrange becomes pretty obvious. Those that say one click (+/-) per 20 degrees, they're pretty close. I find a click, click n a half difference per 20 with my rifles... seems very true
We shot to 820 this last weekend.. 440, 650 and 820 were where I set the gongs. The trajectories in one rifle using H-1000 and one using retumbo both were consistent with the 1 click per 20 statement, charts were adjusted only for temp.. no muzzle velocity adjustment what-so-ever. Good stable powder is a must**
All that said.. I like IMR 7828 actually, as a next best to the Extreme line from Hodgdon... BUT have clocked ~100fps swings using that 7828. Good podwer, but not for long-distances where cold/hot drastic swings take place... fwiw