The English 4 bore shotgun is the equivalent to the US 4 gauge. The black powder gun was popular from 1750-1880 and is nearly obsolete today. It was used to hunt large and potentially dangerous game animals.
English settlers found their muskets inadequate against dangerous African game. 4 bore shotguns were used on horseback where the rider could shoot at an elephant and quickly ride away to reload. This process was repeated up to 30 times until the elephant was dead.
Frederick Selous, a British, settler killed 78 elephants with the 4 bore. His gun would shoot a quarter-pound bullet loaded with 540 grains of powder! Recoil problems, along with a double loading incident, finally got him to give up the gun due to it “upsetting my nerve.”
This video will give you a slow motion view of the gun and explain the specifications.