For what?.... an airgun barrel, like used on the MRod, or a PB barrel such as a .257?.... They are different enough that they do not interchange.... You can only shoot pellets, or bullets designed for the smaller diameter, in a 0.250" airgun barrel.... and you can only shoot bullets in a .257" barrel, pellets are too loose.... LW uses something in between, at about 0.254" and then less at the choke.... designed for pellets only....Bob