Sounds like it will be a fun shoot for sure. At what range will you sight in for with those .457's and what will be your (point blank range) to hit those doggies?
You can see what the roundball does by using the following ballistic calculator. Don't forget to fill in the box in the upper left hand corner (.457 RB will really be .454 when it leaves the barrel so put .454) and filling in SWC will give you an idea as there is no RB setting. Enter a sight height of 1.65 inches Roundball goes 870fps out of my rifle, and I will be sighting in in at 50 yards,
I just arranged to have a bunch of 155grain, and 175 grain SWC's to be cast for the trip as well. I am hoping to see over 800fps with the 175grainers. The 155grainSWC's are going as fast as roundball in some of these rifles.
Knowing the trajectory of this set-up like I do, I can predictably hold-over properly with nice 1 inch drop increments out to about 75yards using a 50 yard zero, and expect a hit if I do my part.
This is a group I shot using 150grainSWC's (these were harder lead, slower, too) off the steady stix real quick one day while sitting down in the field. Scope was a fixed 4X32mm rimfire scope. Off a table with a rest, I should do better.
http://www.handloads.com/calc/index.html 
