NICE -

If nice an tight.
1 1/8 ounce ball weighs 492gr. (437.5 gr. X 1.125)

That is a 14 bore ball, ie: about .690" to .692" for a true 14 bore ball - which is actually 500gr. in pure lead.

A .682" ball in pure lead weighs 482gr.

A slightly harder alloy, used for dangerous game would reduce weight slightly, to the .490gr. range, ie: 1 1/8 ounce.

You should slug - ie: measure the muzzle of the rifled tube, land to land, and groove to groove & use a ball that is appropriate in size, within reason. A .730" ball (583gr.)- true 12 bore might be too heavy and not regulate.

There are several 12 bore loads listed in Greener's book for 2 3/4" shells, 115gr., 150gr. and 191gr. IIRC, without checking.