The OAO Kolskaya Mine-and-Mill Concentrating Plant classification section overflow sampling method for base metals content determination has been improved. Inconsistencies with GOST 14180-80 requirements regarding automatic samplers and sample reducers operation in the 1st, 2nd and 3rd grinding sections were eliminated, coefficients of variation were experimentally determined, in agreement with which classification overflows homogeneity category, required operating characteristics of sampling and sample-preparation equipment, as well as sampling errors, were determined. The measurements performance procedures, approved by the Federal Agency on Technical Regulation and Metrology, were Developed.