AFTE Store - The Effect of Revolver Cylinder Gap on GSR Production and Projectile Velocity

Although the muzzle is the primary source of gunshot residues in revolvers, the cylinder gap is a source of a small amount of very energetic gunshot residues. These emerge from both sides of a revolver just after the base of the bullet passes this location when the internal pressures of discharge are near their peak. Cylinder gap spacing in a properly configured revolver is typically on the order of 0.004 to 0.006 inches. The appearance and location of cylinder gap residues and the spatial relationship of these residues to gunshot residues from the muzzle of a revolver have well-known reconstructive value but it is the possible affect of significant variations in cylinder gap spacing on the residues emerging from the muzzle that were the subject of this research. For this purpose a Dan Wesson 357 Magnum revolver was used. The design of this brand of firearm allows the cylinder gap spacing to be adjusted over a wide range of values. Witness panels placed at fixed distances to the side of the cylinder gap and in front of the muzzle of the test revolver were used to record the GSR deposits at selected cylinder gap settings. A ballistic chronograph was employed to measure the effects of cylinder gap variation on bullet velocity. Small variations in cylinder gap spacing had no detectable effect on muzzle GSR or projectile velocity. Large departures from normal cylinder gap spacing had significant effects on muzzle residues, bullet velocity, and cylinder gap discharge and even resulted in physical damage to the bullets as they transited the cylinder gap.