yes, that what we will try pure tin only.
technical an undersized bullet shoot with a sabot out of a rifled gun barrel is illegal like owning hand grenades here. justification is there will be no traces so the police can't find the gun in case of murder.
I don't know what they doing if you use a slug or shot out in a smooth bore shotgun

We try to investigate if this law is also in use for a 150 years old antique but the ways troughout the bureaucracy are very long.