Smitty,
I load my own slug loads using cast Lyman flat nosed slugs. I load them inside Winchester AA wads and hulls and star crimp them. I tend to load up towards the top end on these because I know the guns will take it, 1500 to 1600 FPS. These are accurate in fully rifled barrels and hit like sledgehammers.
When you buy one of their molds you get the loading data and the recommended powders to use. It's all pretty straight forward and easy to do. Because the slugs are fully protected by the shot cups, I can load dead soft slugs in them that will expand to a very large size. I have one 20 gauge slug that I found after it went though four gallon jugs of water, it is flattened out to the size of a quarter. I do fill the hollow bases with a special wax mixture to keep the wads from being pounded up inside the slugs. Bob