Re: changing zero
yeah there is a difference in hits between temp, baro pressure, humidity, altitude especially at 100yards and with a rimfire that effect the flight of the bullet as the air is "thicker or thinner". where it's zeroed today, may not be the same next month.
i my data book, i generally split the info into 3 seasons:
i usually do my data book in three seasons, summer 85deg. , winter 35deg., fall/spring 55deg. for each caliber
i figure on a cool summer night or day, i refer to the fall/ spring data, if a cold fall or spring night / day i flip to winter, bring it close enough for center mass.
within each season, there is all of the below, going in sequence:
ranging / distance
drop data.
wind data.
then cosine data, if applicable.
there are even more subtle differences, but it gets it in the neighborhood for a center mass type shot or slight adjustments for more precise target shooting.
this is an example of just what the temp of the ammo itself can do:
Effects of ammo temperature itself - not air temp
not only did group size differ, but the POI too.
i'd used to keep data for every 5 degree increment, but it got just too time consuming whipping out the "bible sized" book to look it up, so the seasonal condensing of it made it more convienant, at least for me.
without taking temp and other environmentals into consideration, the results almost get you into the panic mode and asking yourself is it due to the scope possibly being off, is there other damage, etc. at 200 yards, the differences could lead to a several inch difference in POI.
with centerfires at 100, it's hardly noticeable, but with rimfires it starts showing up around 75 yards noticeably.
