A red band usually indicated Z/UF. This was an artillery term for Z= Base Workshop repair only and UF = Unfit to Fire but I have seen it on other things, usually rifles - especially No8 rifles that have multiple bulges in the barrels. I would suspect that this is what's the matter with this pistol. A bulged barrel or deep cut or a pucker as a new barrel can only be fitted to a revolver at Base Workshops. But I could be wrong........