Yes, powder charge and the distance the bullet is off the lands.
I generally start at .030" off the lands and seldom have much reason to change that.
Modern temperature compensated powders are much better. With some older powders, a change of 30 F in barrel and ammunition temperature is equivalent to a change of 1 grain of powder. So trying to fine tune those down to .1 grain is an exercise in futility... unless, of course, your are controlling temperature down to plus or minus 3 degrees F.
I don't shoot 7mm Mag, but I suspect that a 160 grain Partition over Retumbo would be a winning combination. Somebody that has actually tried that combination can give you a better report than I can.
There are a multitude of ways to do it right. Enjoy the trip.
How many man hours are consumed (wasted?) by handloaders meticulously weighing charges for typical deer rifles and shots inside 300 yards?
