Empirical evaluation of spring powered air rifle storage and modifications on forensic practice and casework.

•Storing airguns vertically and/or cocked can statistically affect muzzle velocity.•Airgun modifications can significantly affect consistency of pellet discharge.•Impact on muzzle velocity cannot be predicted by gun calibre, brand or model.•Practitioners should re-consider standard testing procedures for modified airguns.•The industry should consider adopting air pellet standards for muzzle velocity testing.