Seems a little strange but it could be a very early one in which case it should have 6 grove rifling as they very quickly went to 2 grove to reduce production costs
Also the serial number should be proceeded with a number then letter "C"
My No4 MK1 Has 6 grove rifling and has a 4 digit serial number 0C 1753 is how the spacing should be
The cocking piece on the early ones were a button and then they went to the slab rectangle cocking piece
This is the little I know
