A cast metal sideframe for use in a railway car truck has a spring seat for supporting the springs of a spring set. The sideframe is molded using a core that includes a portion for defining the exterior surface of the spring seat. The core can be a single piece or multi-piece core. The spring seat includes a plurality of aerodynamically-shaped spring retainers formed on the top face spring seat. The aerodynamic shape of the spring retainers reduces the tendency for sand to swirl and create voids during formation of the sand core that is used to mold the sideframe. The aerodynamic shape may include forming at least some of the side walls of the spring retainers at an obtuse angle with the top face of the spring seat. The spring retainers may have concave top faces so as to reduce the volume of material comprising the spring retainers. Reducing material volume is beneficial for reducing shrinkage during cooling of the sideframe, thereby reducing the tendency for separation, tears and cracks to form on the top surface of the spring retainer.