IMM - I would cut the shells and save the powder, primers, shot, maybe the wads. Been there, done that a few times.
Loading shotshells is ***SO*** different than loading for most rifle/handgun cartridges. This is Extremely compounded by the lack of shell components with listed shotshell loading data. Best thing is to get trusted advice whence mixing/maxing components in substitute manners. Even so, load maybe 5 shells, test, and look for pressure signs. Good luck, you'll need it ... as with most of us loading shotshells these insane times.