Heterogeneity is an important factor controlling fracture initiation, accumulation, and propagation within rock destruction. Traditionally, rock reaction instability within rock destruction is associated with rock non-homogeneity or considered self-excited, but no clear relations between rock structure options and reaction force oscillation were proposes. This work hypothesizes the idea rock structure options are one of the factors of drill bit whirling. The authors innovated the Wojtanowicz and Kuru’s force static balance model to numerically simulate 3-cutter movement in a rock space, assuming a crack propagates by rock grains getting around. Instability of deviation between directions of cutting force and crack propagation causes rock reaction instability. Novelty of this work is to consider the mutual influence of rock granulomentric composition options (sizes, shape and distribution of grains) and drill bit design options (cutter diameter, distance between adjacent cutters, etc.) on rock reaction force oscillation. The follow tendencies were observed: rock grain dimension increasing and grain concentration increasing were accompanied with rock reaction force magnitude decreasing; random grain placing and/or grain random dimensions caused increasing of rock reaction force scattering; random grain sizes are more essential for rock reaction forces (and their projections) scattering than random grain distribution.