Board Thread:Off Topic/@comment-29684190-20191110024409/@comment-25396609-20191210024257

hrm... Mechanically the transformation would need to be VERY different (A mortar requires a much longer barrel, meaning it would probably have to be located in the haft), and the explosives would be  a lot more... intense.

Based on that, I'd say a hammer or mace is fine; but maybe make it so it can't be fired for melee purposes due to the configuration of the barrel and the fact that doing so would also explode the user.