1 3/4" Mini 12-ga shotgun shells. Aguila mini-shot shells in #7-1/2 bird shot. Great ammo for playing around on the range. 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.