Different kind of powder. Some powders can be multi-purposed, but shotshell powder has a different size/burn rate than rifle and pistol powder.
A person might be able to switch powders and bullets between, say, 115 gr fmj 9mm rounds from different lots to confuse things, but that will only mean all three lots will show up--case, powder, and bullet, and all three would be held accountable for the crime.
Best to just stop this crap from becoming law.
depends on the cartridge. unique is about the most common powder around. you can load just about any pistol with it and it is also used in shotguns. red dot and green dot are also common shotgun powders and can be used as pistol powders.
Some powders are perfectly good for both shotgun and pistol.