I have a 1913 field grade 12 bore. Double triggers and 3 position safety. When you push safety foreward and fire either barrel the safety moves back to safe. You have to push it foreward again to shoot other barrel. If you pull safety to the rear it works as should. It just started doing this. It has not been "worked on" or even taken apart. Anyone know where I should even start to remedy this?

Sounds like the safety spring is broken. Since it is a three position safety what happens when you push the safety to the rear and fire the gun? Also are you shooting hi brass or low pressure loads?

I have a 20ga Ideal grade that did the same thing as describe.I had the safety spring replaced with new old stock spring,it helped but still happened on occasion.I started using low recoil AA's and it has never happened again.