First of all, forget all the data on the web on 200 yard zeroing. In my opinion, the 460 S&W Mag. should be zeroed at 100 yards because that's the furthest most semiproficient handgunners would be comfortable shooting at and with a lot of loads, the accuracy beyond that range is insufficient in my opinion for hunting purposes. Also, take along a box with a target on it or something so you can initially shoot a lot closer than 50 yards for your sighting in. It's entirely possible to completely miss a 50 yard target with a handgun when sighting it in.
I don't shoot Hornady FTX bullets in mine but I would hazard an educated guess that if you were right on at 50 yards you would probably be 2 or 3 inches low at 100 yards. I do know that with mine sighted in to be dead on at 100 yards with a full house load and 250 gr. Hornady SST/ML bullets, the drop from 100 to 200 yards is about 7.5 inches.
By the way, my avatar shows me with my 15 in. 460 S&W and a Klipspringer I took with it in South Africa at a range of about 180 yards.