A French percussion gun with a 27 mm diameter heavy barrel.

[Cerjak]

Originally Posted by fernando

Wow; i have never heard of that; on the contrary, to my understanding, the actual muzzle aperture marks the calibre (bore/gauge) and the bullet to fit there has a narrower diameter... assuming we are talking smooth non rifled barrels, obviously. Why would you have to add one centimeter to quote the gun's calibre ? .

Fernando,
When you using a" pied à coulisse" ,for internal diameter you have to add 1 cm to the mesure shown to have the internal diameter.