Toolmark reproducibility on bullets fired from smooth-bore modified blank firing pistols

The conversion of blank‑firing pistols into lethal firearms represents an increasing forensic and public‑safety concern in both the United Kingdom and Turkey. These weapons, typically lawful at point of sale, can be modified with relative ease, and are now frequently encountered in violent crime. When converted using improvised smooth‑bore barrels, the absence of rifling complicates traditional microscopic projectile comparison. This intravariability study examines whether bullets fired from such weapons nonetheless retain reproducible, source‑informative toolmarks suitable for comparison. Fifty‑nine converted pistols submitted to the Istanbul Gendarmerie Criminal Laboratory were assessed. In each case, the factory dummy barrel had been removed forward of the chamber and replaced with a section of tubing to create a smooth‑bore. Nominal bore dimensions included one at 6.35 mm, fifteen at 9 mm, and forty‑three at 7.65 mm. Test‑firing was conducted using full‑metal‑jacket ammunition in 6.35 mm Browning, 7.65 mm Browning, 9 × 17 mm, and 9 × 19 mm calibres. Bullets from 41 of the 59 pistols (≈69.5%) displayed reproducible toolmarks that were sufficiently consistent to support comparative examination. The most informative features were parallel, longitudinal striations extending from base to nose, indicative of firm, consistent bullet-bore contact. Although mark quality varied with the apparent smoothness of the bore, coherent linear detail across multiple axial regions supported robust same‑source conclusions. In the remaining 18 pistols, predominantly cylindrical and shifting patterns prevented reliable alignment, resulting in appropriately inconclusive findings. Practically, microscopic comparison of projectiles from these weapons should be actively considered in casework, with triage prioritising regions that exhibit longitudinally continuous linear striae across the bullet's length.