Many moulds have a slightly smaller front driving band. It seems more prevalent in Lyman moulds. The reason for this is to allow easier chambering in revolvers when there is a little fouling at the throats. Elmer Keith ripped Lyman several new a**es for doing this to several of his mould designs. I have had difficulty chambering cast bullets with full diameter driving bands in competition before. The reduced diameter driving band does make it easier, as does a slightly shortened front band, However, it can also reduce bullet alignment to the throats, and make the front band more prone to skid when it engages the rifling. It doesn't surprise me to see this in a wadcutter mould, my 358432 Ly man mould also has a reduced front band. My two RCBS wadcutter moulds are full diameter, and are a couple of my other Lyman moulds.