AFTE Store - Lead Density on a Target: A Significant Indicator of Firing Distance, but is it Reliable?

Shooting distance is currently determined by visual observation of the pattern developed by color tests such as the Modified Griess Test (MGT) and Sodium Rhodizonate test. Although these tests are based on empirical research, they are qualitative and subjective. Several measures have been proposed that quantify one or more components in gunshot residue (GSR), providing a basis for reporting certainty and an error rate, including measuring the lead density in defined rings around a bullet hole. Atomic absorption spectroscopy (AAS) was used to measure the lead around the bullet hole in targets shot at distances of 15, 30, 45, 60, and 75 cm (5.9, 11.8, 17.7, 23, and 29.5 in), using several combinations of firearm and ammunition. Linear regression models relating the density of lead (ln dPb) to firing distance were used to calculate the firing distance of samples shot at known and unknown distances. The accuracy and precision of the calculated distances varied with the brand of ammunition used. However, even though coefficients of determination ranged from r2 = 0.92-0.98, at the 95% confidence interval, 17-29% of the distances predicted from the calibration curves were rejected as incorrect. While there is a strong correlation between dPb and distance, more research is necessary.