After 50 years I have found my first shotgun. Marlin model 90- f-3301. The last thing I remembered about it was that both barrels fired and knocked me down. After cleaning, removal of the stock to oil and grease I had the same problem. If I fired the front trigger first and then the rear everything was ok. But if I fired the rear trigger first and then the front, both barrels went off. This time it didn't knock me down but left me a black and blue shoulder. Does anyone have any suggestions. Thank You. To tell you the truth, I no longer fear recoil after this experience and went out and bought a Moisin 31/59.