Yes. Caliber is measured land to land.So by caliber they must mean the bore diameter, not the groove diameter?
The wording of the regulation is.
The holder of a small game licence may not use a rifle of
greater calibre than .275, except a flintlock or percussion
cap muzzle-loading gun, for hunting small game in the
counties of Brant, Elgin, Essex, Huron, Lambton, Middlesex,
Northumberland, Oxford, Perth and Wellington and
the regional municipalities of Chatham/Kent, Durham,
Haldimand-Norfolk, Halton, Hamilton-Wentworth,
Niagara, Peel, Waterloo and York and the City of Toronto




















































