Consider Rifled Slugs in the 1970's:
Twelve gauge rifled slugs were originally smaller than bore diameter, with most running to .690 - .695 inches. It was only in the late in the 1970s that Winchester increased the diameter of its rifled slug ammo to the nominal 12 gauge bore diameter. Federal followed soon after. Remington held out, making undersized slugs into the 1980s. So, these sub-diameter rifled slugs were the norm from their mid-1930s introduction well into the 1970s and were considered minimally accurate only to 60 or so yards. Indeed, the Ithaca Deer Slayer, introduced in 1951, was produced with a reduced bore diameter to match the diameter of rifled slugs at the time. The Deerslayer, alone among contemporary deer shotguns, delivered usable 100 yard accuracy with the heavy undersized soft lead thimbles.