When inputting a ballistic coeficient there are 2 different ratings a G1 and a G7. Which one should I use? I was loading the info for the SMK 155 palma #2156. Thier websight lists it as .504. When I compared identical info with JBM there was an inch and a half difference at 300 yards. I did notice that JBM changes it to .298 or something after you calculate for drop. What am I missing or messing up?