Assume you mean scoped rifle? In that case I agree with most posters here, 350yds give or take is starting to get long range. Archery obviously different. When my uncle passed away and I got his Colt Python handed down to me, I decided to deer hunt with it in his honor. With an iron sighted 357, I felt 50 yards was pretty long range.
like some others have said, the deciding factor is the moment I have to think about anything other than settling the crosshairs right on and getting a solid trigger press. Another rule of thumb I use as well is if I have to modify my shooting position anything other than standing to get solid on it. Using both of these methods, Its usually within 200 yards