Every firearm, even the most powerful of magnums, start falling the MOMENT it leaves the barrel. The velocity it leaves at and how long it maintains its velocity, determines how "flat shooting" the gun is.

Fact: There are no "flat shooting" muzzleloaders, esp when compared to high powered rifles. However, with the load you are shooting, you have a relatively flat shooting load.

If you sight in to be dead on at 100 yards, you will beABOVE the bullseye at 25, 50 and 75 yards.

Here is a link that will get you in the ballpark: http://www.powerbeltbullets.com/ballistic.html

Just look up 295 gr. powerbelts, and 100 grains of pyrodex. Your load with 100 gr of 777 should be slightly more powerful than that (aprox 15% more).

If I were you, I would try for a dead on sight in at about 75 yards. If you do that, you will not even have to think about it from 0 to 100 yards, just aim where you want to hit, and shoot. However, if there is a chance of going out to 120 yards, sight in at 100 and you will be fine from 0 to 120.