The 5R rifling is asymmetrical in both the number of rifling grooves, and their shape. The theory is that odd number of grooves results in the bullet being squeezed less - any groove is not diametrically opposed in the bore by another groove, but rather by a pair that are spaced apart from each other. The asymmetrical groove shape seems to reduce fouling from bullet material. The 5R is found desirable by the long-range shooting crowd, although not universally so. If most of your shooting is at normal hunting ranges (say, 300 yards or less), I think you'd be hard-pressed to see an advantage to the 5R barrel.