Declarations of war have been essentially obsolete since the Second World War. Since the formation of the United Nations, wars of aggression are explicitly an international crime. An official declaration of war could be evidence in a war crimes trial. By not issuing official declarations anymore, governments make it easier to defend themselves on the basis of "it wasn't really a 'war'" or "we were just defending ourselves."

Technically they would not be "rifles" because the bullets require smooth-bore barrels. It might be time to resurrect the term "musket" for the weapons that fire these rounds.