Using the same powder charge and bullet weight in a 45cal creates more pressure than the 50cal. Its pretty easy to see if you have some conicals of the same weight for a 45 and a 50. Shoot them both over a chrono with about 70gr of powder. You will probably need over 80gr in the 50cal to match the velocity of the 45 using 70gr.
Hodgdon lists over 100fps difference with some loads when comparing 45 to 50.
https://www.hodgdon.com/wp-content/uploads/2017/01/muzzleloading_manual_2008.pdf
