Computations using a one‐dimensional computer program have been performed to determine fragment mass distributions for exploding cylinders of HF‐1 steel. Experiments were performed to guide the computations. Nucleation and growth models were used to simulate the brittle fracture and shear band damage that occurred in the metal cylinders prior to complete fragmentation. Material input parameters for these models have been previously determined. Computations were performed for two heat treatments of HF‐1 steel. The calculated brittle crack and shear band distributions were converted to fragment mass distributions using one of the experimental fragment shapes. Based upon the experimental results, suggestions are made for future refinements in the area of fragmentation modeling.