I found some 720 grain cast, gas checked .458 bullets on ebay and was wondering if anybody has had any experience with these. I am considering trying some in my .460 Weatherby but I have no idea where to begin or what performance I should expect from these. I plan on making these into plinking rounds so performance on game is not a consideration.
Thank you.

Even at plinking velocities those things should prove to be un-stoppable. I use 680 gr cast bullets in my 505 Gibbs at 1400fps and they out penetrate anything short of, and sometimes including, good solids

I would keep the velocity low with those 720's as they will be loooooooong, and long bullets in a standard twist barrel can be unstable.

My .460 Weatherby started out as a CZ 550 American Safari Magnum in .458 Lott so, I may be wrong about this, the barrel should have a faster twist rate than Weatherby rifles. Does anyone have any idea of where I would start loads with these? If not, are there any good programs out there that will point me in the right direction? Thank you for the help.

Sounds like the slugs I use in a 45-120, they come from a mould for the 460 Weatherby, there tuff to stop.
Don't have any smokeless loads for you