Just looked back over my sources again. You're right: The legality depends on the type of rounds used, and their effect on soft tissue. Plated rounds are legal, it is unjacketed lead bullets that are unlawful, as unjacketed shots expend or flatten upon penetration of the human body. This makes the bullets almost impossible to get out without causing further suffering or death by exsanguination. Other nations have declared the use of shotguns unlawful, however, as they provide no real means of military advantage while causing unnecessary suffering. Basically, what theyre saying is that you shouldn't have to use a shotgun when any other weapon works just fine without being as inhumane.