The bore of a gun can be examined by:-
Helixometer: An instrument for inspecting the interior of a gun barrel and for measuring the rate of twist of the rifled bore of a firearm. Comparison microscope is used to match the marks in test bullet & crime bullet Broach cutter is used to produce riflings in a gun.
Broach cutter
Helixometer
Comparison microscope
Simple microscope
Ballistics