Assuming you are using a carbide sizing die, you just screw it in til it touches the shell holder, then back off about an 8th of a turn. Ready to go. You don't want the carbide sizing ring touching the shell holder, as carbide is hard, but brittle, and can crack when forced against the shell holder. Being a straight wall case, the sizing die basically just slides down the length of the case, sizing it back to factory specs, allowing you to seat a bullet with the needed bullet pull (friction) to hold it in place. The crimp seals the deal. Just like a bottle neck case, you should use a slight flare to the case mouth to assist in seating the bullet. The case headspaces on the rim. Trimming is important, as you will have a hard time getting consistent crimps with cases that vary in length. Even though you are shooting in a single shot rifle, you still want to use a crimp when loading the .500 with slow burning powders, as powders like 296 and 110 need a heavy bullet crimp for proper powder burn. Strait wall cases tend to stretch less then bottleneck cases, so trimming is not needed on every firing. Just sit there and visualize what each step is doing, and it becomes pretty clear after a few loadings.
Larry