I have an old wm Powell side by side box lock which i have owned without fault for 20years and it has been serviced regularly. Today I had a misfire in the first barrel whereby the cartridge primer had a light strike but did not go off. This happened again and I then fired the cartridge successfully in the second barrel. I do have a local gunsmith that I can use. Before I speak to him do you have any suggestions as to what the problem could be? Pin? Springs? This will help me ensure I get the best service locally.