The only ported shotgun I've seen was John Satterwhite's 870 which he used for exhibition shooting. IIRC, after 18 years, it had four rows of holes--two rows on each side of the vent rib. They appeared to be *about* 0.050" or so in diameter. I think each row had maybe six or eight holes. The rows were just behind the screw-in choke.
Were I going to do something like that to an 870 barrel, I would have no qualms about doing it myself. I have a dual cross-feed workpiece holder for my drill press. Scribe the line, carefully center-punch, and drill.
It sure seemed to work for Satterwhite, given his shooting seven hand-thrown claybirds with it.
Art
