Re: Possum Hollow Bore Guide for Rem 260
I think a #4 would fit better. The outside should be the same (.308 body), but the bore of the bore guide will be smaller to give less wobble on the rod. #4 fits Remington Centerfire for "243, 6mm Rem, 257 Roberts, 25-06 Based cases & 6.5x55 & 22-250".
Actually, I noticed you didn't say which action you were running, so you may need a different one. Check out their chart, but I think that's the right category for .260.