Shotguns:

     The shotgun is unique in that the ammunition components are contained within the shotshell and a plastic wadding. Since most shotguns are smoothbores, the only component that is contact with the barrel is the plastic wadding.  This makes shotgun ammunition extremely difficult to identify to a specific weapon. 

       The six photos below depict a typical shotshell being fired.  The plastic wadding containing the pellets leave the muzzle.  The plastic wadding begins to peel back as the pellets continue.  Eventually they will spread out.  The plastic wadding can continue travel as far as 72' or further.  I gratefully acknowledge Prof. Andrew Davidhazy (www.rit.edu/~andpph/exhibit-shotgun-blast.html) for permission to use these photos as a display.

Revolvers:

     Revolvers come in numerous calibers.  They have rifled barrels which the projectile remains in contact with as it leaves the cartridge case and spirals down the barrel.  These rifling marks, land and grooves, are imprinted into the bearing surface of the projectile and leave microscopic toolmarks which may identify a projectile to a suspect revolver. 

     Cartridge cases can usually be identified through forensic microscopy by comparison of the breechface markings and/or firing pin impression. 

     Contrary to popular belief, the majority of revolvers have one or more safety's.   The claim of a revolver being dropped and accidently discharging can be quickly proven or disproven by the experienced ballistician or firearms examiner.

    When a revolver is fired there is not only a muzzle blast, some of the gases escape from the small gap located between the cylinder and barrel.  The following photo depicts the discharge of a revolver, the barrel/cylinder gap gases are visible.

Pistols:

Pistols are commonly thought of as semi-automatic.  There are single shot pistols and machine pistols.  Most modern pistols have safeties engineered into the design.   There are manual safeties, magazine safeties, grip safeties, etc.