AFTE Store - Spectrophotometric Determination of Time Since Discharge of Firearms

A new approach for determining the time since discharge for firearms (shotguns) up to twenty (20) days after discharge is described. Previously our Institute had solved this problem with a technique based on electon spin resonance (ESR). The basic principle in the ESR method and the present method is the same and involves the estimation of the time-dependent degassed concentration of nitric oxide (NO) from the bore of the firearm after discharge. The nitric oxide is produced by the burning of smokeless powder. The determination of the nitric oxide concentration inside a gun barrel is carried out with a special selective indicator at different intervals promptly after receipt of the firearm in the laboratory. The kinetic curve of the selective indicator’s concentration versus time is measured with a spectrophotometer in the UV range each day until the degassing NO from the bore of the gun ceases. The measured kinetic function is ultimately compared with the analogous one obtained for the evidence gun after a controlled firing and plotting of its specific NO decay curve.