Cubed Shot.
Back in the day one used to get cubed shot her in the South, and I have forgotten what the brand name was.
Some local fellas that made bullets, made cubed shot as well.
At one time a Distributor I knew, would get Fiocchi reloading components, so I have used Fiocchi primers, nickel plated shot and the rest of the Fiocchi components to reload.
Again, fixed choked gun, folks knew what a gun did, by actually patterning their gun.
Cubed shot opened up, and was the chambered shell for flushing quail for instance and a fixed mod or fixed full barrel would the shotgun . Cubed first, second shot a load of target (hard shot) for when the quail were out a bit.
Dove shooters with O/U and SxS, especially double trigger guns, on a dove coming in to them, would slap trigger on hard shot chambered barrel on the second dove further out and then slap trigger on cube load for the dove right on top of them.
This ain't no mantle piece , this heres a using shotgun...