This is coming from a website page martinihenry.com/faq.htm
After W.W.I, the Egyptian Government sought a weapon suitable for arming their police force. W.W. Greener won the contract with their submission of a handy, smoothbore Martini actioned shotgun with a full length wood forend. These shotguns were known as the Greener Mark I/14. The “14” referred to the bore size. One of the clever features of the new shotgun was that it used an off size 14 1/2 gauge straight sided shot shell. This prevented the weapon’s use with commercially available shotgun shells. Thus, if the weapon fell into the wrong hands, it couldn’t be used against the Egyptian Police. Greener referred to this cartridge as “14 bore for use in Mark I guns”. These cartridges were made by Kynoch. . By 1922, over 30,000 Greeners had been supplied. In the 1930’s, it was discovered that stolen Mark I’s were being used against the authorities by wrapping a thick piece of paper around standard 16 gauge shot shells. Greener answered this problem with the Greener Police Gun Mark III. The Mark III was chambered for three different shells: the original 14 1/2 gauge Mark I shells, standard 12 gauge 2 3/4" shells and a special bottlenecked shell for the Egyptians. The Mark III bottle necked shell was .782" diameter at the base, and was necked down to .740". Overall length of the shell was 2 7/8".
has anybody info on the 14 1/2 Gauge ?
I asked to the website owner but he never repplied .