I'm considering buying a Sharps rifle. I can't decide if I would rather have the 45-70 or the 45-120. I realize that the 45-120 will kick like a mule, but I'm a little concerned about the ballistics on the 45-70. With such a heavy bullet (405grn) and little powder, this thing will drop like a cannon ball. But, if I went with the 45-120 (500 grn) which is a bigger bullet, could I expect a better trajectory than the 45-70's?
Has anyone had any experience with these gun's? This gun is the same type used in "Quigley Down Under"

The downside is that 45-70 cartridges and brass would be much easier to find than 45-120's.

I'm sure the action of the Sharps imposes some pressure limitations, but my Ruger #1 45/70 will fire a 400 grain Barnes spitzer at 2270 feet per second, if I am in the market for some real punishment!! That seems to be enough powder capacity for me!!