Crime Scene Balistics

[ajacobs]

In the spirit of a couple of recent threads, that were trying to figure out how well we knew our hobby, I have a couple of questions that have been puzzling me. These all stem from my addiction to those darn crime scene shows they show on discovery/A&E/ Court tv etc.

1. From a recovered projectile can they tell what type of cartridge it was fired out of? Obviously they can tell a 45 from a 9mm but what about telling between various .30 cal rifle rounds, can they tell it came from a .308 and not a 30-06 or a 7.62X39 and how? What about a 9mm and .38 or 10mm and .40. They both have could have the same weight, and outside diameter correct?

2. How certain can they be when they say a bullet came out of a given gun? If I took 10 barels from a glock for example and fired one round out of each and the barels all came out of the rifling machine one right after the other could they really tell which came from which? Or are they just able to say that projectile is consistent with one fire from that gun. My guess is they can becuase of the multiple threads about the FBI rounding up replacement Mak barels.

3. Same as question 2 but with cartrige cases. I know the ballistic fingerprinting is no good becuase it changes over time and you could change it with a couple or file marks but that aside, how sure can they be?

4. Is it just our luck that things like glaser's and lead free fraginable (sp) have not been banned as they would not have any way to tie them to the gun correct? Of course they would not have that with a shotgun either all though I have read that each batch of powder is somewhat unique and they have matched half a box of shells in someones possesion with the powder residue in a cartridge case at the scene.

I am just curious as in all these shows and probally in jury rooms across the country they lead you to believe this is 100%.

 

[Pilgrim]

Question 1: No, not really. They could hazard a guess, but it would be highly speculative. When muhammad and malvo were shooting up Virginia and Maryland, the police said they were looking for a .223 caliber rifle, but the bullet is really a .224 caliber and could have been from a .222, .223, .220 Swift, .22-250 cartridge.

9mm and .38 are not the same bullet. 9mm is .355 in diameter. .38 or .357 Magnum are .357 or .358 depending on if the bullet was jacketed or a cast lead bullet.

Question 2: Maybe, maybe not. Two barrels cut one after by the same tool might be difficult to differentiate. The more apart they are the more likely it is to match a bullet to a barrel. Each pass with the rifling tool changes it a little bit.

Question 3: Firing pin, ejector and extractor marks, and chamber marks on cartridges change little over a long period of time. The forensics examiner is counting on the likelihood a crook is not likely to fire thousands of rounds to alter his weapon or use tools to alter the same.

Question 4: You make a good point about bullets that thoroughly break up on impact. I guess there have not been enough homicides with these to attract the attention of the chuckie schumers and teddie kennedys of the world.

TV shows would be unbearably long if they took the time to explain all the problems and pitfalls with ballistically matching bullets and cartridges to guns.

Pilgrim

 

[BluesBear]

Regarding #2, It's not always easy to determine that a bullet came from a certain barrel. It's rare that the bullets match up perfectly like you see on TV.
It's like fingerprints, if you have enough areas that match you can say it's the same.

Fired from the same barrel a lead bullet can have different striations from a copper jacketed bullet or even an aluminum jacketed or steel jacketed one.


#4
It's not at all uncommon to have a regular hunting type rifle bullet or an expanding handgun bullet that is so deformed by impact and or medical procedures that it can't be positively identified. I have personally seen 9mm & .45acp FMJ that struck bone or other barrier and were too deformed to do a ballistic match.

 

[Langenator]

Can they tell from the marks made by the rifling what manufacturer/type of gun fired the bullet? Say, just to mess with the cops, a hit man killed someone with a S&W 610 revolver, but fired a .40SW instead of the usual 10mm.

1. Could they tell it was a S&W, not a Glock, Sig, SA, etc?

2. Could they tell it was a .40SW, not a 10mm?

 

[popbang]

In order of your questions

1. To point you can tell what it may have been fired from. A .224 FMJ with a cannelure is consistent with a 5.56mm. Depending on the identification of the bullet it may only be loaded by a manufacture for a certain caliber, an example would be .357 Sig bullets, which share the same diameter as the 9mm, but could be identified if you could conclusively identify the bullet.

2. A case is not made solely on finding a ballistic match. You must have other support for the case then ballistics is brought in to solidify the case.

3. Marks on a case are fairly consistent when firing the same type of ammunition. Different brands of ammunition will result in slight differences in the marking patterns. What they are always looking for is ammunition in the suspects possession that matches that found at the scene and when fired through the suspected weapon produces the same markings.

4. Markings found on fragments can sometimes be identified depending on the size.

You can identify some types of firearms be the rifling imparted onto the bullet, an example of this is the polygonal rifling. This may not be conclusive, but it can be used to show that the evidence is consistent.

You can through all of these statements out if the perp uses handloads or understands the issues as you could create an example that would not be consistent.

 

[carpettbaggerr]

Could they tell it was a S&W, not a Glock, Sig, SA, etc?

Read about a shooting where several cops fired on a perpetrator. Coroner asked " who had the Detective Special?" All but one were using Smith&Wessons. Colt's rifling is backwards, so they knew exactly which shots he had fired.

 

[BluesBear]

orensic examination of a fired bullet will reveal the;

Caliber
number and width of lands & grooves
direction and rate of twist

This information can be used to narrow the field of possible firearms that could have fired the bullet.

 

[Langenator]

Another thing I thought of: how does forensics deal with shell casings that have been reloaded, especially ones that have been reloaded multiple times after having been fired from different weapons?

 

[BluesBear]

There would be a fairly strong breech face imprint since the latest would partially obliterate the previous ones. Resizing wipes away most of the previous chamber markings.

In the case of a semi-automatic you'd have multiple extractor & ejector marks that they may or may not be able to identify.

In all cases the firing pin imprint would be the best indicator since it would be the singular most unique feature.

 

[Archie]

Sometimes.....

1. From a recovered projectile can they tell what type of cartridge it was fired out of? Obviously they can tell a 45 from a 9mm but what about telling between various .30 cal rifle rounds, can they tell it came from a .308 and not a 30-06 or a 7.62X39 and how? What about a 9mm and .38 or 10mm and .40. They both have could have the same weight, and outside diameter correct?

Works best with factory loaded rounds. F’rinstance, a GI 7.62 NATO round has a 147 grain boattail bullet. A Warsaw Pact 7.62x39 has a 124 grain bullet. M1 Carbine has a 110 FMJ.
9mm, Super 38, 38 Special and 357 Magnum bullets are built differently. A 158 grain RNL is uniquely a 38 Special projectile. 124 grain FMJs are 9x19. 130 grain FMJ is Super 38.
The next factor is the twist and direction of twist. Typically, a .38 Special has a slower twist than a 9x19. So by looking at a combination of type of projectile and twist characteristics, one can develop a pretty good idea of what cartridge was fired.
Compare an empty case from a Glock to about anything else. Glocks have the dangedest looking firing pin mark I have ever seen.
In the Muhammed-Malvo murders, the police said they were looking for a .223 caliber rifle. Typically, (surplus or commercial) .223 ammo has 55 grain FMJ bullets. Sometimes a 55 grain SP in commercial ammo. .22-250 are typically 50 grain SP. Also, the police won’t normally release all the information they have. They want to be able to dismiss the chronic confessors, and they don’t want the suspects to dump the rifle and use another.

Yes, handloading can confuse the issue. One could load a pulled 7.62x39 bullet in a .30-30 case and confuse folks a bit. Or shoot 255 SWC 45 Colt bullets out of a .45 ACP revolver. (Then leave 10mm empty cases laying around... he he....)

2. How certain can they be when they say a bullet came out of a given gun? If I took 10 barrels from a glock for example and fired one round out of each and the barrels all came out of the rifling machine one right after the other could they really tell which came from which? Or are they just able to say that projectile is consistent with one fire from that gun. My guess is they can becuase of the multiple threads about the FBI rounding up replacement Mak barrels.

Barrel markings are pretty individual. They do change with use, but guns used in crimes are not typically “hobbyist†guns. (Except for Platt and Matix... oh, well....) Yes, barrels can be identified.

3. Same as question 2 but with cartridge cases. I know the ballistic fingerprinting is no good because it changes over time and you could change it with a couple or file marks but that aside, how sure can they be?

Pretty much the same answer. Breech faces and extractors and firing pin tips (in that order) are rather individual in terms of machine marks. Yes, they change over time, but not instantly.

4. Is it just our luck that things like Glaser's and lead free frangible have not been banned as they would not have any way to tie them to the gun correct? Of course they would not have that with a shotgun either although I have read that each batch of powder is somewhat unique and they have matched half a box of shells in someone’s possession with the powder residue in a cartridge case at the scene.

Again, factory loaded ammo often has a non-commercially available powder that can be distinguished. But even Glaser’s and the frangible ammo types have distinct weights. And Glaser’s leave a jacket that can be re-assembled and analyzed for diameter and such. Counting up the fragments will tell something. Frankly, I’m not worried about shooting someone and not having everyone know what happened. Self-defense may be on the agenda, but murder is not.
Of course, one could load ammo to penetrate the target and then find the bullet before leaving the crime scene. But that could be problematic... “Murderer caught dismantling wall!†or “Shooter identified by stolen tree in back of car!â€

The short answer is (now I tell you), yes, the forensic programs are pretty authentic. The ones on the Discovery Channel are more accurate than CSI, but CSI has to make a story out of it.

 

[TheeBadOne]

Just watch CSI...it's all real world stuff...