1 3/4" Mini 12-ga shotgun shells. Minibuck shot loads with 7 pellets of 4Buck and 4 pellets of 1Buck at 1200 fps. Low-recoil and a great choice for home defense. Works well in Winchester 1300 and FN shotguns. Remingtons and Charles Dalys may require some modification. Mossbergs require some elevator modification. I have had some success with this load in a Benelli Nova.
For further information: Aguila Ammunition Minishells.