All firearms are dangerous and should always be considered loaded.  The "empty" firearm is the one that kills or maims. 

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.  Ocassionally defects left in the barrel may impart markings on the plastic wadding but microscopic comparison is usually not successful.  When a shotgun s fired, the pellets are pushed outward against the plastic wadding and form indentations that most often override any oddities left by a defect in the barrel.  The most common procedure to identify a specific shotgun to a crime is if the shotshell was left at the scene which can then be compared to test firings using ejector, extractor and breech face markings.  Markings might also be available from the loading process.  Although not common the markings made during manufacture might identify a shotshell to other shotshells. 

     Shotguns can cause massive wounds and damage.  Barrel lengths are usually between 18" and 32".  At the muzzle shotguns have a constriction known as a choke.  Some are manufactured into the barrel permanent and others are adjustable or can be changed.  Chokes help keep the pellets together as they exit the barrel. 

     Shotguns are available in an array of configurations:  side-by-side double barrels, over/under double barrels, double barrels with an added rifle barrel, single barrel.  The single barrel can be a break open single shot, pump action, semi-automatic, rotary magazine equipped, tubular magazine, etc.   These firearms can be modified by sawing off the barrels ("sawed off shotgun"), shortening the buttstock, or both.   There is a vast supply of aftermarket parts available for shotguns. 

     Shotshells are available in different lengths with 2 3/4" and 3"  being the most popular.  These sizes are the length of the shotshell after being fired.  Within these shell lengths are numerous sizes of pellets and slugs, and there can be differences in the amount of pellets loaded into each shell.  The most popular guages are .410, 20 ga., 16 ga., 12 ga., and 10 ga.

   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 can be utilized to identify a projectile to a specific revolver.  During tests in the 1980's I test fired five Smith and Wesson Revolvers off the assembly line which were sequentially manufactured.  Each revolver imparted unique and distinguishable markings, or striations, which were identifiable to that specific revolver only.  

     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.   Pistols are a very complex firearm which should be handled with extreme care.   One of the most important considerations of semi-automatic pistols is that the trigger pull is greatly reduced when the weapon is cocked and ready to fire.   Their age, condition, and amount of use can be prime considerations when there is a claim of accidental discharge.  It should be remembered that when there is a claim of accidental discharge then examination of the weapon should be conducted in a manner so as not to alter the condition it was in at the time it discharged.     

 

Rifles: 

There are literally hundreds of calibers for rifles.  Barrels are rifled with lands and grooves which impart microscopic toolmarks or striations onto the bearing surface of the projectile as it transverses the barrel.  Cartridge cases can have toolmarks imprinted on them through the loading and extracting, firing pin impression, breech face markings, and chamber marks.  Although rare, factory ammunition can have bunting marks which can be compared to other ammunition to ascertain if it was manufactured on the same machine.  Rifles can range from basic BB Air Rifles to .50 caliber class.

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