Some "Experts" say that 3.5 lbs is the floor for field guns. Sounds OK to me. My GM has a 4 lb trigger, my Model 94 has a 4 lb trigger, a couple revolvers here have 4 lb triggers SA.
I do have a couple guns with much lighter triggers, but they are not used in moving situations or crowds.
A note, those who do not think a clean light trigger is important on a shotgun go try the trigger on a couple Local Legends' pets. With their permission, of course. Bet the usual flagon of mead they're light and clean.