3" 12mm shells had been available in England for some time prior to 1933
http://cartridgecollectors.org/?page=collecting-410-shotshells And I agree we'll need documentation in the surviving Hunter Arms shipping (unfortunately not order) records to confirm originality
BTW: "Shooting Around The Clock" was conceived in 1923 by William Harden Foster, who was then editor and chief illustrator of both
National Sportsman and
Hunting and Fishing magazines. The discipline became "Skeet" in May 1926 and was aggressively promoted by Foster.
By the mid-1930s the .410 was being used in competition in two classes: ".410 Long" with 3/4 oz. and ".410 Short" with 3/8 oz. shot.
