Well, yes and no.
When I loaded for the 500, it was for a Handi-Rifle. I even used sabots with 44 caliber cast bullets inside of them. The powder was Trail Boss and the load was the same as other loads using this powder. Fill the case up to the bottom of the bullet, in this case sabot, and go from there.
As for the "slugs" you are talking about, and only shotguns shoot those, are you talking about lead bullets designed for the 50 caliber muzzle loaders? If so, then the answer is no, don't use them unless they are held to under 1000fps. You will not like the lead that they leave behind if you try to send them out of the muzzle any faster than that with smokeless powder. They are much softer than a hard cast bullet.
The whole sabot thing is something that I worked up all on my own. I don't think I would try it in a handgun with a cylinder gap, no matter how small.
The principle is the same for some 30/06 accelerators though. They use a 22 caliber bullet in a sabot inside the neck of the 308 caliber sabot.
FWIW