MICROMETER-SIZED PARTICLES OF RESIDUE FROM THE BULLET, COATINGS OR JACKETS OVER THE BULLET, AND INGREDIENTS IN THE PRIMER ARE LEFT ON THE HAND WHEN A PERSON FIRES A GUN. THESE PARTICLES HAVE A CHARACTERISTIC APPEARANCE UNDER A SEM. WHEN COMBINED WITH X-RAY ANALYSIS TO DETERMINE THE METALLIC COMPOSITION OF THE PARTICLES, THE SEM CAN INDICATE NOT ONLY WHETHER A GUN HAS BEEN FIRED BUT ALSO THE POSSIBLE TYPE OF AMMUNITION USED. THIS STUDY ANALYZED THE RESULTS OF SEVERAL HUNDRED SMALL ARMS FIRINGS TO DEVELOP CRITERIA FOR IDENTIFYING THESE PARTICLE PATTERNS. THE RESULTS ARE PRESENTED AS A NARRATIVE AND AS A SERIES OF TABLES GIVING BULLET COMPOSITION, BULLET JACKET OR COATING, AND PRIMER FOR THE MOST COMMONLY ENCOUNTERED HANDGUN TYPES. (THIS JOURNAL ARTICLE IS A SUMMARY OF A COMPLETE REPORT WHICH CONTAINS FULL TEST RESULTS AND WHICH IS WRITTEN FOR USE AS A TRAINING MANUAL.) PHOTOGRAPHS ILLUSTRATE VARIOUS PARTICLE PATTERNS WHILE A CHART SHOWS THE RELATIONSHIP BETWEEN NUMBER OF SPHEROIDAL PARTICLES AND MUZZLE VELOCITY. THE CHARACTERIZATION OF GUNSHOT RESIDUE HAS BEEN FOUND TO BE ADEQUATE FOR SUCCESSFUL ANALYSES OF ACTUAL CASES. (A SECOND REPORT DISCUSSES INDUSTRIAL RESIDUES WHICH MAY BE CONFUSED WITH GUNSHOT RESIDUE -- SEE NCJ 57028.) REFERENCES ARE APPENDED. (GLR)