7/8 and 1oz are standard 20 bore loads from way back as they are today. Today as well, we have a 1 1/4oz. 3" magnum load. The 7/8oz load is pretty much a 'square' load, that being the shot charge is roughly 20 bore long and 20 bore wide, sitting in the barrel. This charge of shot will give the shortest shot string - the more shot you put in, the longer the shot string. On a passing bird, ie; duck, grouse or pheasant, the longer the shot string, the less pellets of the shot cloud that are available to put on the bird. Where one throws a disk of pellets, the other throws a strung out cloud with fewer pellets able to hit at any time. On stationary targets, the long shot string makes no different - it's on moving targets that escape due to few pellets passing at any given time - huge holes in the cloud of pellets.