Sorry to be the bearer of bad news.
The other day when I first shot for speed over the magnetospeed I said it was 33 degrees. In reality the Ammo and gun went into a warm car out of a warm house. So I'm guessing that I was getting 3200 at around 65 degrees.
Today with the same load of 73grs. with the gun and ammo at a blistering
-7 degrees below zero, I lost 100fps and the groups went to crap.
My Retumbo and 168gr. CC still bug holed so twasn't me or the gun.
Back to the drawing board.
My chronograph strings are suggesting the opposite with IMR7977 with 270 and 243.
I have not had the opportunity to chrono in really warm weather vs cold weather. But with temps at about 60 degrees vs high 20's there is no difference with identical loads and componets other than well within normal variation. I haven't mentioned my results because I wanted to wait until I had info that included temps from hot weather (like 80's or 90's ) vs cold weather (single digits).
Knowing what the temps of the firearms, ammo and air is important. Cold/heat soaking the firearms and ammo, and operating the chrono in a warmish enviroment is important too.
What brand of chrono were you using? Did you keep it warm during cold weather? Was the firearm and ammo heat/cold soaked?
Casey
