An experimental apparatus using cooling slope and thin metal container has been developed to study controlled rheocasting process. The microstructural characteristics of Al-8%Si industrial alloy processed by this route were determined statistically. The statistics and quantitative analysis of the dispersions of particle’s diameters were used for process optimization. Emphasis is placed on factors which determine the final grain size in a billet. It is suggested that much of the refinement of the microstructure in the process may be caused by temperature fluctuations in solid shell formed at cooling slope. The nuclei which could be formed by melting of eutectic phase in solid shell and transferring by overheated liquid metal to the container mostly survived and contributed to final globular microstructure of a billet and ring type feedstocks.