I have two no-dash 617s, a 6" and a 4". The 6" shoots tiny groups with the Federal Game-Shok 38-grain copper-plated hollow-point (Federal load #712) and the 4" likes that load and the Federal Lightning 40-grain solid (load #510) equally well. Neither gun shoots well with Remington, Federal or Winchester target loads and the 6" shot its worst groups with the Remington target ammo. I've never tried any of the "good" imported target ammo as the Federal 712s shoot better than I'm able to and will work great for the occasional small game hunt.

John, you might want to try ammo with copper-plated bullets in your 4" to see if the leading clears any.

Ed

Forgot to add that the deposits left on the cylinder face by the Federal ammo wash right off with bore solvent and an old toothbrush. Most ammo requires a brass brush and an abrasive cleaner like Iosso GunBrite.