.22 BB

The .22 BB Cap is the round Louis-Nicolas Flobert built in 1845 by seating a plain lead ball directly onto a percussion cap, without any propellant charge of its own — the priming compound alone drives the ball, at very low velocity and with almost no report, which is the entire point of a parlour or gallery cartridge meant for shooting indoors. “BB” here has nothing to do with airgun BBs; it stands for “bulleted breech”, describing the ball seated in the case mouth, and the round is sold across Europe under the name 6mm Flobert.

Its later relative, the .22 CB Cap (“Conical Bullet”), shares the same tiny case but replaces the round ball with a conical bullet and a small charge of propellant, giving it a touch more velocity and range while remaining about as quiet. Both are considered the same cartridge under the 6mm Flobert name in Europe, but they are catalogued as two distinct American products, and only the BB Cap fires a plain round ball with no powder charge at all — the defining mechanical difference between the two.

Every dimension in this entry comes from the C.I.P. datasheet for “22 BB Cap”, which lists no maximum pressure figure at all. Wikipedia’s infobox gives three bullet weights, all cited to the book Cartridges of the World, which cannot carry a verified status without a clickable source, so only bullet mass is recorded for each and no velocity or ballistic coefficient appears here.