Taylor built a 1" bore Underhammer bench rifle for a fellow. It weighed 51 or 52 pounds. Smooth, no rifling.
He also made a mould for it & we cast up a bunch - right around 4 bore weight, or 1,750gr.
With 300gr. of 2F, if moved back 1 foot on the sand bags, no matter how "much" shoulder you put into it.
We were able to shoot about a 3' group on the 300meter sand/rock/dirt berm. It seemed to move about
1/2 yard of dirt every shot. That 300gr. charge is only 11 drams. That is almost 3/4 normal charge for
a 4bore smooth or rifled SxS of English make, for shooting elephant near the end of the 19th century.
They used "up to" 16 drams, or 437gr. with round or conical ball.