Assumptions and simple maths. It would seem reasonable to assume that the “English” copies of the military Girandoni are of similar proportions to keep the overall look. If this wasn’t the case then why bother to make them look similar. They could have just put the same mechanism in one of their own design air rifles. The tubular ball magazines on the side of the rifles being the same length, for appearance sake, the accepted military calibre of .51” Girandoni had a stated capacity of 20 and Lewis and Clarkes had 22 as described by Rodney when shown it. Why? A good guess would be that the Lewis and Clarke rifle was a civilian copy of the Girandoni which are usually of smaller calibre.
20 .51” balls in a row equal 10.2”.
22 .46” balls in a row equal 10.12”.
Probably just a load of balls but the thought occurred to me as I was having a good long soak in the bath
. What do you think?