A process for preparing polyvinyl pyrrolidone modified, high crystal density, very-fine crystal nitramine explosives selected from cyclotetramethylene tetranitramine and cyclotrimethylene trinitramine and mixtures thereof having sufficient shock and impact resistance to meet military safety standards as well as having a positive surface charge which comprises (1) dissolving the nitramine in a solution of polyvinyl pyrrolidone in N-methyl-2-pyrrolidone, (2) precipitating the resulting polyvinyl pyrrolidone-modified nitramine crystals into cold water, (3) filtering the resulting suspension, (4) treating the resulting filter cake with a solution of polyvinyl pyrrolidone in 95% ethanol, filtering and drying the resulting filter cake at about 80.degree. C.-90.degree. C. to remove the ethanol and water and (5) recovering the resulting modified very-fine crystals of nitramine explosive.