Sounds like a description of the Hartin crimp, but the shortened star is tight against the card and the hull has a roll to the edge of the hull...Properly done it should behave like a roll crimp. However black powder needs more compression than modern smokeless and that may explain loss of pressure.

https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=610808&page=1