I taught that course at Ft. Gordon. we called it “quick kill” it was based on the old Lucky McDaniels method “quick point”. Trainees could usually hit a salt tablet thrown in the air by the End of the day, no sights, front or rear. some could hit a bb 3 out of 5 times. I Later wrote a piece on it for American Shotgunner. That said, I put a rear sight on my 28 ga/56 cal Fowler for hunting for the sake of responsibility. I shot some matches with it and could do fine, in position, with a consistent cheek weld etc. in good light. But hunting often involves weird angles and lower light.. so in the interest of humane shot placement, I use sights. Can’t compete with that gun anymore, but that’s OK.My smoothbore was built with a rear sight installed. I just shoot it like a rifle with both ball and shot. The gun shoots really well, so outfitted.
At Army basic training back in the 1960s we trained with BB guns sans sights. Good work could be done the slick barrel guns even on flying targets.