Are you guys shooting over cold cronos? Does that make a difference? It was only 15 below when I woke this morning. I might do some cold weather shootin tomorrow if I have some time.
A chrono isn't cold until the display quits working
They get a little slow to put up the number around -20. I've had to pull the battery out between strings and keep it in my pocket before.
I'd done lots of cold weather testing a couple years ago. You get about a 28 FPS swing with Varget in a 308 over a 120 degree spread (I've chrono'd it from -30 to 90 degrees)
Of the combo's I've tested H4350 and RL19 in the 260 rarely are over 50 FPS on a 80 degree spread
Varget in a 308 with 165s and Federal 210s isn't worth worrying about
and H4350 in a 30-06 with 180s varies less than 50 FPS.
RL15 in a 308 and 338 Federal varies very little...
IMR4350, the spreads just about double in the 260 and 30-06 (AA4350 is even worse)
7828 in a 243 with 100's will drive a guy nuts...
Federal LR primers seem to help cut the spread down (compared to CCIs offerings)
I'm undecided on TAC and Xterminator in the ARs over big temp spreads. I've got lots of conflicting data over the years. I eventually settled on H4895 behind Sierra and nosler 77's for a Highpower load (even though TAC can push them a little faster) I figure testing them between -20 and 70 degrees is a bigger swing than I'll see during season. H4895 with Federal SR match primers in Lapua brass has a spread of ~55-60 FPS in a 20" tubed AR.
