Ed

Here are the dimensions of the 4 Bore

Imperial Cartridge. Brass

Length with bullet 4.832"
Length 4.259"
Diameter of rim 1.192"
Diameter of case at rim 1.091"
Thickness of rim .17"
Diameter of case at bullet 1.275"
Diameter of bullet .835"

Kynoch. Paper Shotgun

Length 3.891"
Diameter of rim 1.19"
Diameter at rim 1.078"
Thickness of rim .175
Diameter of case 1.022"

Loaded with BBs

marked Eley-Kynoch 4

These are loaded rounds. Not having a 4 bore I haven't shot it too get an empty case.

The Imperial Cartridge cases were loaded as recently as 10 years ago and they may still be available. They were a limited run for a pair of 4 bore singles made by London Guns in Melbourne Australia.