Hmm, three .33" buckshots arranged in a triangle over a .73" slug, sounds just like a Revolutionary War loading for the Brown Bess or any of the large-caliber buck & ball cartridges supplied during the American Civil War.
Combining buckshot and a bore-sized ball in a single charge is a historical and very effective answer to improving the lethality of the smoothbore in combat.
One unit, the 12th New Jersey Infantry, was so effective with their smoothbore .69 Springfield muskets so loaded, that they became known as the "Buck & Ball Regiment." The typical 69-caliber, paper-wrapped musket cartridge of the day contained three buckshot over a single roundball and was not a load you wanted to be facing if within 200 yards of the shooter.
Winchester's Supreme Elite PDX1 loading for the 2-3/4" 12 gauge is composed of three, copper-plated 00 buckshot layered in Grex buffering media over a 1-ounce Foster-type, Power Point slug--a real hammer load, clocking 1,150 fps.
At 15', (left) the slug and three buckshot formed a centered group of 3-1/2" with the wads flying out into the 9 ring.