I think with open sights a big factor is the distance between the rear and front. Some of my pals have been in the Bulgarian army and are quite confident hitting stuff at 100 yards with an AK (that's vanilla flavour open sights).I was in the Israeli army and 200 yards with an M16A2 doesn't sound infeasible. I mean, the manual says the peep sight can be adjusted for 300 and even 800 meters, lol! And it's not substantially different than an open sight - just a little bit more length between rear and front.Now scopes... I guess if you buy a scope and adjust if for post-open-sights range (200 yards) and then you try shooting something at 20yards, you'd be at quite the underhold! (depending on gun/pellet too).But under/over holding with a scope should be easier than doing that with open sights
300 yards with an m16 and open sights is a lot easier than 30 yards with a springer