Daryl,
Thanks for the comments. I do own a Marlin 450 Lever gun but that is not what I am referring to. The gun I wish to load for is the Eagle Arms BFR a 5 shot revolver (10 inch barrel). Throating is a concern with the rifle but in this handgun the cylinder is quite long and throating is not a concern. I can set the 500 grainers out quite a ways without interferring with the function of the gun. I don't know why it did not dawn on me before...of course the 458 x 2" data would be a really good place to start.
xring