The .40 caliber mold is a .400 diameter so I am guessing that since this rifle was a slip fit true bore, the bore size would be .400. Also this rifle weighs over 12 pounds, so it is not going to be something you would want to carry around all day long. BUT if you were on stand, and had a good rest, from what I have read of the Gibbs rifle accuracy, you would have a real long distance rifle there.

Again, some states do not allow that caliber for deer hunting. It would be fun to own just to try and do some distance shooting. I see Pedersolli sells the molds for the rifle as well. So you would cast your own conicals. I would guess these are some very large conicals.