When aiming a flintlock or percussion rifle, the hammer is on strong side or outside of the gun, and like most people I close my weak side eye. I always tell new shooters who are worried about seeing the hammer that if you are practicing good fundamentals and focusing on the front sight post, you won't pay any attention to the hammer. It won't be in the way of your sight picture and it shouldn't distract you when the gun fires. This mostly applies to shooting rifles or smoothbores at a stationary target when you are aiming the rifle, as opposed to pointing a shotgun.
I don't have any experience with double guns and what I want to know is, when shooting a double barrel smoothbore as you would a shotgun when you are pointing at a moving target (rabbits, birds, clays, etc), do the hammers impede your sight picture? In other words, does having a hammer on both sides of the gun obstruct your field of view or interfere with picking up the target?