if it is not rimmed then it is either 7x64 brenneke which goes back to 1916 or 7x61 sharp & hart which is around 1946 ,and rigby did make guns in this caliber mike schwandt has one on his web site as we speak .if on the gun it just says "high velocity" this means 140 grain bullet in 275.rigby or(7mm mauser} ....paul