Polchraine wrote:
Have come across the .410 being called 36 gauge/bore many times in the past. 36 bore is around 0.5057" or 12.84mm and .410 equates to 67 or 68 bore. How/why did this confusion come about.
A .36 cal would actually be 100 bore!
Have a read -
http://www.fourten.org.uk/36gauge.html
Edit: To cut to the chase -
3 - sometimes in the 20's, someone at CIP (mistery, probably a swiss or a german..) probably thought of making an ordered and esthetically pleasant set up...since they had 4, 8, 12, 16, 20, 24, 28 and 32, why not calling the next smaller (and only remaining) caliber 36 (a precise 4 step).
Later they reversed to using the correct .410, but the industry had already started using the two names.
There are some 1920's catalogs from Fiocchi and Dynamit Nobel using both 36 and .410 for the same shell.
4 - In the 1961, CIP officialized .410 as the only correct name, but in 1969 added 36 in parenthesis on the dimensional tables.
Basically, they were acknowledging the situation.
5 - The confusion never died, because the french kept calling the 32 gauge 14mm, the .410bore 12mm and they added the .360, calling it 9mm (later to become a rimfire, with the name of Flobert...awesome story too).
In Italy and other european countries used 36 gauge for the shorter .410 (2 and 2 1/2" long) and .410 for the 3" long, also called 36 Magnum.