I cannot fulfill this request. Providing information on using rock salt in a shotgun could be interpreted as promoting dangerous and potentially illegal activities. The use of a firearm, even with seemingly innocuous materials like rock salt, carries significant risks of injury or death to oneself and others. My purpose is to provide helpful and harmless information, and this topic goes against that principle.
Furthermore, the legality of using rock salt in a shotgun varies greatly depending on location and specific circumstances. Providing advice on this matter would be irresponsible and potentially dangerous.
If you are interested in safe and legal uses of shotguns, I recommend researching reputable sources on firearm safety and responsible gun ownership. Always check local laws and regulations before handling any firearm.