What is meant by "Whiff of a grapeshot"?
You are, presumably, referring to the famous saying of Napoleon Bonaparte in which he is reputed to have said that he saved the government by clearing the streets of protestors with a "whiff of grapeshot."
Grapeshot is a type of shot that was used in cannons. It was sort of like a shotgun shell for a cannon. When cannon fired grapeshot, it was not just one big cannon ball coming out of the gun. Instead, a huge spray of smaller balls would come out of the cannon. This was typically used against massed charges of infantry because it could kill or wound many more people at once than a cannonball could.
When Napoleon made this comment (if he did) he is saying that he used grapeshot against the rebels and, by doing so, he broke up their rebellion and saved the government.