anyone have problems with jbm?
i ran some numbers over the jbm calculator and i dont trust the results i got.
i wanted to see a comparison of shooting a 208 amax in a .308 and a 140 vld in a 260ai and several unusual things caught my attention.
first thing that caught my attention was when i was entering the info for the temp i would be shooting in i always type in either 100 or 0 degrees for shooting year round, however, when i hit the calculate button i looked at all the info and the temp was always 59.2 degrees no matter what i did.
second thing, i used the g7 bc for both bullets[.324 for 208 amax and .313 for 140 vld] and when i calculated it showed up as .648 g1 bc and .612 g1 bc. and yes, i checked the g7 box and it still showed up as g1 both times.
third thing, and this is the most confusing for me, the .308 shows a whopping 212 ft-lb difference at 1200 yds [867.7 for the .308 and 655.5 for the 260 ai].
heres the confusing part, how can the 260 ai have that much less energy when the bullet is starting out 200 fps faster and the bc's of both bullets are nearly identical.
heres the numbers i inputted into jbm
velocity-2750 for the .308 2950 for the 260 ai
altitude 1312' asl
std. atmosphere at altitude box checked
i appreciate any and all input you guys and gals can give me