The U.S. Bureau of Mines is conducting research to develop blast designs for the control of fragmentation and rock displacement and the reduction of overall mining costs. This Bureau experiment, a program of 25 reduced-scale blasts conducted at the University of Missouri--Rolla's experimental quarry, determined the effects on fragmentation of changes in burden, spacing, explosive diameter, and stemming-explosive length. Combined with previous work at this experimental quarry examining air gap, delay, and decoupling effects, this experiment provided a data base of over 50 shots. The fragmented rock, 1,000 to 3,000 kg from each three- to four-hole blast in the 1-m bench of massive dolomite, was completely screened to assess fragmentation. The explosive used for all the tests was extra dynamite initiated by seismic caps fired from a sequential blasting machine with delays of 5.2 to 13 ms per meter of burden. Empirical equations were developed that predicted the effect of shot design parameters on the fragmentation. These formulas predicted the average fragment size of each of the 25 shots to within 13 pct. For spacing-to-burden ratios of 1, 1.4, and 2, there were optimum burden-to-explosive-diameter ratios (b/de) of 30, 26, and 20, respectively. Decreasing the b/de ratio beyond these levels resulted in little or no reduction in the average size. For b/de ratios above these levels, the average size increased, but at least a 15-pct reduction in the average size results when the shot design parameters are optimized.