The gun in question is a 1906 12 ga. F grade hammer gun. Not a joint check model, but one of the last versions of the hammer models. I suspect, but do not know, if Hammerless barrels will fit on this frame.
In an ideal world, the "Barrel Exhange" page would have a form to complete, including spaces for all pertinent data. The concept could also be expanded to include all manner of parts. This could free up the Forum for sharing all the other information folks are interested in.