Well, I used to be an ordained nuclear physicist but now that I'm retired I'm just a grunt. You pretty much got the right idea though, the gun has the same mass but the heavier bullet and powder charge impart more rearward force to make the barrel pivot up quicker which gives a higher initial bullet trajectory. The initial higher trajectory is pretty much used up by 50 yds so lighter bullets at similar velocities will print higher at 100 yds.