Thinking of shells, casings and guns. I have watched too much NCIS, its true.
Feel free to correct me or add anything I may be missing as I attempt to understand.
Lets say someone shoots a gun, the gun spits the casings out and the bullet s go into a fencepost.
For whatever reason BCI gets the gun, casing and shell.
Am I understanding correctly that they can identify the shell being fired by this weapon due to markings on the bullet as it gets fired from the gun, that said gun absolutely fired the bullet?
Ive studied the research involved with how LE tries to identify weapons involved in shootings and I can share what I know about it.
Its real interesting and LE can identify certain weapons used in shootings but it is very dependent on what items they can recover from the crime scene. LE can only be successful if what they uncover is the right things and they are in a condition that is good enough for them to identify.
We first have to be sure to understand the 4 main parts that LE needs to try to find at the scene or after the crime.
1-THE BULLET
Bullet is the lead or other metal type projectile that comes out of the shell casing and hits a person or thing like a wall. The bullet is what kills and lands inside a person.
Its very important to know that bullets deform and break apart many times after impact with things. So depending on what LE finds of the bullet will impact how much they can identify things.
The markings on the bullet occurs from the gun's barrel as the bullet travels down the barrel. Each barrel will leave unique microscopic markings but if the bullet is broken apart or fragmented into pieces then identifying a gun is either very difficult and sometimes impossible to use the bullet. Sometimes just tiny fragments of the bullet is all LE finds.
If LE finds a good intact bullet then if they also find the gun they can do comparison tests as they shoot new bullets through it to tell if the same gun shot the bullet they found.
We are talking about microscopic tests for markings so certain markings may only be seen at microscopic level and can be very unique to a gun and what its particular barrel does to every bullet that goes through it.
Criminals have been known to file the inside of barrels after a crime to disrupt the markings after they commit a crime so that if LE finds the weapon it wont leave the same markings the next time.
2-SHELL CASING
Shell casing is the housing that holds the bullet. There is gunpowder and a primer that is part of the shell and is what causes the explosion to force the bullet out the end.
Only semi-automatic handguns throw the shell casings out. If a person has a revolver with a cylinder then the casings stay with the gun. Criminals are getting smart and will sometimes pick up their shell casings after a crime.
Rifles typically always throw out the shell casing if another shell is cocked into the chamber.
The shell casing is very important to find too because LE can compare the small microscopic markings left by a guns ejection system and they can sometimes tell if a gun is the same gun that ejected a casing.
I had one gun a long time ago that left bad scratches every time I ejected a casing. The casing markings were very visible on that gun. LE uses a microscope and detect small minor markings on casings from the ejection system of a gun.
3-THE PRIMER
Primer is the small round mini explosive that sits on the end of the shell casing. The hammer of the gun lands on this primer and a mini explosion takes place which causes the gunpowder to explode and the large explosion to make the bullet projectile force out the other end.
The primer is important because the guns hammer will leave a mark on the primer. Each gun will leave very unique hammer markings on the primer. So if LE can find the shell casing then they have 1 part of what they need. They will also need to find the gun to compare the markings when they test fire new shells through the gun.
4-THE GUN
The gun with the barrel attached(either handgun or rifle).
LE has to eventually find the gun to have something to compare to. This is why criminals sometimes throw them in lakes rivers etc. They know the gun is important to LE to find so they take steps to get rid of it.
Handguns have many types and depending on the type then LE can get more evidence or not. Semi-Automatics throw the shells casing. Revolvers do not.
Rifles usually throw casings if another shell is cocked into its chamber.
Criminals are getting smarter and most criminals now try to not leave shell casings or the gun around after they commit a crime. The bullet projectile is usually recoverable but it can be deformed or broken into pieces and so the bullet may not be much help to LE unless they find a good intact bullet to compare markings to,
The bottom line is LE needs to find as much evidence at the scene as possible which includes the shell casing, the bullet projectile, and eventually the gun itself is always needed to have something to compare to.
Hope this helps.
