Last Wed. I started loading for a new rifle I got in 260. I loaded 42 grs of 4350 pushing a 139 Lapua seated at 2.80 OAL. It was averaging 2,830 fps. The temps were around low 70's. yesterday I shot those same loads and was averaging about 3,011 fps. Temps were aroun 68 with 60% humidity. I'm shooting over an el cheapo Chrony but why would the velocity change that much? About a month ago I shot some Black Hills 175s over that Chrony and the rounds were pushing about 2,650 fps. The next week I shot round from the same box that were about 100 fps faster than the week before. Temps were close to the same. Gonna try a different chronograph when I get the chance but was wondering if anyone has had this problem.
Thank you.
Thank you.