I trained with open sights years ago 1960s...first deer rifle had those nice buckhorn sights and hooded front (Marlin 336 New Haven manufacture). Nice buck came along while hunting in the beautiful Northeast woods - still within legal shooting hours - ...couldn't pickup the sights in the dimming light and had to pass on the shot.
Installed fixed 4x Weaver K4, and didn't miss again. Never shoot at a running Whitetail (slow trot or walk is ok), and take note that your rifle will not drill straight through brush. Take good clean shots with a scoped rifle of adequate power and you'll be rewarded with venison through the off season.