Q: Dear Science-Minded 100 Hour Board:
Here is one that has been bugging me since I had a friend ask me this question and could not provide a good answer.Often in television crime and law shows they flout the crime scene investigators ability to match individual recovered bullets to the guns that they have been fired from due to distinct markings that are left behind on the fired round from the rifling in the firearm. Furthermore, they claim that each and every firing pin (the part which strikes the primer, setting off the cartage) leaves a distinct mark on each spent casing. With how much reliability can crime scene investigators match guns to bullets and casings? I'm skeptical of this science due to the precise manufacturing standards that modern firearms seem to be subject to, and the many variables (such as powder and lead fouling in the barrels) which undoubtedly alter the effects a gun has on rounds (altho very slightly) each time a round is fired. Is this hype that "CSI", "Law and Order", and every other crime show on television in love with grounded in sound practice, or is it another hollywood-hyped fairytale? Hope you are up for the challenge!By the way, roast beef sounds great right now! :)
Sincerely,
Grissolm
A: Dear Purveyor of CSI Myth,
This is a tricky one. Because the answer is yes AND no. Let me dive in a little to help you some.
First off, obviously most TV crime dramas are exaggerated. You have people like Horatio Cane solving crimes, making arrests and even leading a SWAT team into a den of Columbian drug lords (while wearing shades). If my public servants were able to wear Prada and drive Hummers I'd be a little PO'd. So it throws out the window police procedure, reality and even common sense. Then all the available technology (real or imagined) is there at the push of a button. So we obviously take this with a grain of salt.
But...there is some truth to ballistic forensics. Ballistic forensics is made up of four parts: internal, transition, external and impact ballistics. These are fairly obvious, and lead to examples like laser targeting, trajectory, distance to victim, etc. You are interested in internal, the path through the gun.
Ballistic fingerprinting (or better ballistic signature) is the science (yes a science) of matching a bullet and/or casing to the gun that fired it. First the bullet type is identified to rule out gun types (.22 cal from a .22cal gun, etc.) Bullets do leave striations (lines and markings) caused by travel down a barrel. Typically these are unique to gun type and manufacturer. Smith & Wesson has a right turn rifling in the barrel that leaves distinct marks, number of turns per inch, etc. These can help investigators narrow down gun type. Or even better, eliminate guns from consideration (not the weapon used). You are generally correct, manufacturing methods make reliable grooves from barrel to barrel. However, polishing can't always take out imperfections and wear can affect the look of the bullet. So 'fingerprints' can change over time. This CAN help identify guns.
But bullets are often deformed. Cartridge identification is even better - because they are intact - and can identify make, model, etc.
Generally ballistic fingerprinting gives a: yes, no or maybe answer. And variations in all of the above can lead to a distinct matching of firearm to bullet. But forget databases. The two that are functioning (Maryland and California) have yet to solve a crime (according to the Maryland State Police and CADOJ).
These signatures can be altered and 'cleaned up' but not every criminal is all that smart. (They still don't all wear gloves). So...yes it can be very effective. But it isn't the over-exaggerated 'reality' portrayed by Jerry Bruckheimer.
(Yes this is an overdo response. The 100 Hour Board apologizes for the delay in answering and will do better next time. Please don't put the bullet fingerprinting to the test b/c of this!)
Regards,
Mac Taylor
Here is one that has been bugging me since I had a friend ask me this question and could not provide a good answer.Often in television crime and law shows they flout the crime scene investigators ability to match individual recovered bullets to the guns that they have been fired from due to distinct markings that are left behind on the fired round from the rifling in the firearm. Furthermore, they claim that each and every firing pin (the part which strikes the primer, setting off the cartage) leaves a distinct mark on each spent casing. With how much reliability can crime scene investigators match guns to bullets and casings? I'm skeptical of this science due to the precise manufacturing standards that modern firearms seem to be subject to, and the many variables (such as powder and lead fouling in the barrels) which undoubtedly alter the effects a gun has on rounds (altho very slightly) each time a round is fired. Is this hype that "CSI", "Law and Order", and every other crime show on television in love with grounded in sound practice, or is it another hollywood-hyped fairytale? Hope you are up for the challenge!By the way, roast beef sounds great right now! :)
Sincerely,
Grissolm
A: Dear Purveyor of CSI Myth,
This is a tricky one. Because the answer is yes AND no. Let me dive in a little to help you some.
First off, obviously most TV crime dramas are exaggerated. You have people like Horatio Cane solving crimes, making arrests and even leading a SWAT team into a den of Columbian drug lords (while wearing shades). If my public servants were able to wear Prada and drive Hummers I'd be a little PO'd. So it throws out the window police procedure, reality and even common sense. Then all the available technology (real or imagined) is there at the push of a button. So we obviously take this with a grain of salt.
But...there is some truth to ballistic forensics. Ballistic forensics is made up of four parts: internal, transition, external and impact ballistics. These are fairly obvious, and lead to examples like laser targeting, trajectory, distance to victim, etc. You are interested in internal, the path through the gun.
Ballistic fingerprinting (or better ballistic signature) is the science (yes a science) of matching a bullet and/or casing to the gun that fired it. First the bullet type is identified to rule out gun types (.22 cal from a .22cal gun, etc.) Bullets do leave striations (lines and markings) caused by travel down a barrel. Typically these are unique to gun type and manufacturer. Smith & Wesson has a right turn rifling in the barrel that leaves distinct marks, number of turns per inch, etc. These can help investigators narrow down gun type. Or even better, eliminate guns from consideration (not the weapon used). You are generally correct, manufacturing methods make reliable grooves from barrel to barrel. However, polishing can't always take out imperfections and wear can affect the look of the bullet. So 'fingerprints' can change over time. This CAN help identify guns.
But bullets are often deformed. Cartridge identification is even better - because they are intact - and can identify make, model, etc.
Generally ballistic fingerprinting gives a: yes, no or maybe answer. And variations in all of the above can lead to a distinct matching of firearm to bullet. But forget databases. The two that are functioning (Maryland and California) have yet to solve a crime (according to the Maryland State Police and CADOJ).
These signatures can be altered and 'cleaned up' but not every criminal is all that smart. (They still don't all wear gloves). So...yes it can be very effective. But it isn't the over-exaggerated 'reality' portrayed by Jerry Bruckheimer.
(Yes this is an overdo response. The 100 Hour Board apologizes for the delay in answering and will do better next time. Please don't put the bullet fingerprinting to the test b/c of this!)
Regards,
Mac Taylor
Additionally, in Canada they have a 
Regards,