If I were doing that, I would leave the fired primer in place and epoxy a cardboard wad in the end. The blanks from my father's funeral a few months back were roll crimped like a revolver round but much further. I don't know where mine are or I'd post pix. We split them up amongst family members.
Anyway if your dies do roll crimp, that would work too but I'd certainly add epoxy in the end to seal them. If he wants to fire off ashes for scattering, a shotgun would be better if not proper...
Tony