Average is a pretty broad term. While one would think the additional complexity of boring 5 or more chambers and alligning them with the barrel would hinder the accuracy of a revolver, the plus is the sights are fixed on the barrel and frame vs. the semi which for most designs has a barrel that is not fixed to the frame and a chamber that is necessarily cut to allow reliable feeding from a magazine.
To me good handgun accuracy is 1" at 25 yds, very good is 1" at 50 yds and exceptional is 1" at 100 yds. I expect one is going to find that a quality revolver is more likely to be shooting the very good and exceptional groups than a semi. In fact I don't think I've ever heard of a 1911 shooting 1" at 100yds, revolvers have shot that well.
