The determination of how far a firearm was from a victim or target when it was discharged is a frequent request to crime laboratories. This determination requires test firing the firearm at various distances to compare gunshot residue patterns made during the test with patterns on the victim or target. Crime laboratories stipulate that the same firearm and ammunition used in commission of the crime must be used for this testing; however, little empirical evidence exists supporting this requirement. It was the purpose of this study to determine if there were any significant differences using different firearms and different ammunition in distance determination testing. The findings indicated that no significant differences occurred with different firearms but there were significant differences with different brands of ammunition.