WW296 and H110 are not the right powders to use for light loads.
I wouldn't worry about the XTP bullet standing up to pressure as you are looking at lighter, reduced loads in the .500. Matter of fact, be mindful of minimum velocity needed for that bullet.
I don't own a .500 mag but I do have a .50 Special from Hamilton Bowen. It's designed for pleasant, lower pressure loads and my powders of choice are Unique and 231.