My son's Model 37 had the same problem. Took it to my gunsmith, the gun needed to be disassembled and cleaned of all the powder residue that had built up in the receiver and he polished the chamber. Works fine since the complete cleaning and polishing 15 years ago. Every year I completely take apart my sporting clay O/U and complete clean the gun, it amazes me how much powder residue and burned powder flakes that get sucked back pass the firing pins and the underbite locking flange.over the course of a year and maybe 5000 rounds.
