I got this shotgun from by dad and I use to compete with at my school. After competing for a bit I realized I need to get a modified choke for trap shooting. Looking futher into I cannot find the right size choke to get for my specific gun. Its a navy arms brand and has a skeet and improved cylinder currently in the over and under. The choke is 1 5/8" in length and the thread starts towards end of barrel, 5/8" away from it. I cannot find these dimensions in any brand to buy a choke.