A method of molding reinforced polymer compositions using a molding machine with a tapered bore is provided. The method has particular application in molding polymer that is reinforced with particles having an aspect ratio that is greater than 1:1. The plunger machine used in the method includes a barrel housing with a smooth walled barrel with longitudinal fins projecting inwardly towards the center of the bore that defines a main melt chamber. A plunger housing, having a plunger bore, defines an initial melt chamber and is in communication with the main melt chamber. A plunger resides in the plunger bore and is reciprocatable therein. The barrel bore is continuously inwardly tapered and cooperates with the longitudinal fins to provide a shortened melt period and a smooth transition and alignment of reinforcing members within the polymer mixture during the melt process. The method of using a machine with a smooth bore and cooperating fins ensure substantial alignment of the reinforcement members with the longitudinal axis of the bore in the direction of the composition flow to avoid excessive breakage of the reinforcing particles and prepare the polymer mixture for extrusion into a mold assembly.