First, welcome aboard.
I'll start the ball rolling on the reloading question.
Generally, the theory is that lead develops less pressure than jacketed for a given velocity, due to the lead getting through the barrel easier. So using jacketed data to reload lead is generally on the safer side. Going the other way, well I would say depends.
The closer you are to max book loads for any recipe, the more I would worry about interchanging data. But one should never be jumping to max loads without working up, so if laddering loads, this should not be a concern. I would also be a little more apprehensive if using extremely fast powders. And I would also keep an eye on the length of the bullets you are interchanging, if one is substancially longer from the crimp groove to the base. The more you crowd the powder space, the higher pressures will be for a given charge.
I am actually sorting this exact situation currently with my 454 using a new to me barnes 250 grain XPB bullet. When looking at Hodgdon's data, the Barnes XPB data is definitely using less powder as compared to another traditional jacket/lead core 250 grain bullet, for a given pressure. Surely it is a combination of length of bearing surface, material and case capacity.