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Barrel Length - The length of a barrel as measured from the muzzle to the standing breech in a break-open gun or to the bolt face in a bolt-action rifle, including the chamber. A revolver barrel measurement does not include the cylinder, only the barrel itself.
On a rifle, you would measure from the back end of the barrel to the front tip of the barrel. What and where the stock covers is irrelevent. You include the firing chamber which is where the shell sets when it is actually being fired.