It may have changed here since I last checked. There is or was no specific language stating the legality of shotguns with slugs for big game hunting. There was the .243 (6mm) caliber minimum and a minimum shell length. Shotguns with slugs were not specifically mentioned anywhere in the regulations.up until a few years ago, the only legal cartridges were shotgun slug, .44mag, .357 and .50 I don’t think there was ever an ammo limit until they added other cartridges with only limit being .243/6mm diameter or larger .......that change in legal equipment however only applies to hunting private land
One fellow formerly from Vermont was interested in using a shotgun in dense timber where the shots were close and quick. Upon asking a Game Warden about the legality of using a shotgun with slugs, the Game Warden asked him if the slug diameter was bigger than .243. When the hunter responded yes, the next question was: Is the cartridge length more than 2" long? Again the answer was yes meaning that shotguns with slugs were legal to hunt big game with.