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Old 06-16-2012, 19:20   #1
Henry's Dad
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Forensics question: 9mm vs 357SIG

Here's a question that's been on my mind lately:

If a forensics team extracted a slug from a shooting victim, or a wall, or ballistic gelatin, etc., and the slug remained intact, how would they be able to tell if it came from a 9mm or a 357SIG firearm?
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Old 06-16-2012, 19:30   #2
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Usually the .357sig bullets are slightly different than 9mm bullets. They could also get some idea of how fast the bullet is going but the expansion, damage and etc. If you load the exact same 9mm bullet into a .357sig and load it to 9mm velocities they are never going to be able to tell the difference. Well unless you leave the spent case at the scene. IMO I think some of these forensic ballistics people flatter themselves a little too much as to how reliable the data collected from only a bullet is. Primarily when it comes to tool marks.

Last edited by dkf; 06-16-2012 at 19:30..
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Old 06-16-2012, 20:01   #3
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Your standard 9MM has a rifling twist of 1 - 9.84. The 357 Sig has a standard 1 - 16 twist. A lot of 9MM after market barrels are 1-16, though.

Pick up a handful of projo's from your range's backstop, and you can tell the difference between the two rifling twists.
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Old 06-16-2012, 20:26   #4
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Your standard 9MM has a rifling twist of 1 - 9.84. The 357 Sig has a standard 1 - 16 twist. A lot of 9MM after market barrels are 1-16, though.

Pick up a handful of projo's from your range's backstop, and you can tell the difference between the two rifling twists.
I thought rifling might be the easiest way to tell the difference, but Glock seems to use the same rate of twist in the 17 and 32. And as you mentioned, many 9mm barrels may be 1 in 16.

So, discounting twist rate and assuming "standard" 9mm bullets were loaded in the 357SIG, how else might one determine if a slug was fired from a 9mm or 357SIG?

If it had a 1 in 9.84, you could say it was a 9mm. But if it was 1 in 16, you couldn't say definitively, as it might be either.

I'm just wondering about this from a CSI perspective. What would the forensics people look for in order to tell the detectives, "hey, your shooter used a 9mm (or 357SIG)."
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Old 06-16-2012, 20:49   #5
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What the other guy said, unless you recover the bullet or the case it would just be a guess thought they may get a general clue from the side of the entry hole.

Last edited by cowboy1964; 06-18-2012 at 17:59..
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Old 06-16-2012, 21:12   #6
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Wouldn't the same question exist for the .38 Super?
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Old 06-16-2012, 21:14   #7
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Wouldn't the same question exist for the .38 Super?
Pretty much. You could add the 9x25 to that list as well.
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Old 06-16-2012, 21:19   #8
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Wouldn't the same question exist for the .38 Super?
I think the question in your example would be whether forensics could tell if the bullet was fired from a .38 Special or .357 Magnum.
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Old 06-16-2012, 21:38   #9
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They would just pick up fired brass, read headstamp and ......




Someone had to say it.
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Old 06-16-2012, 22:51   #10
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They would just pick up fired brass, read headstamp and ......




Someone had to say it.
But if the shooter(s) didn't leave the brass at the scene how does forensics determine the caliber?
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Old 06-16-2012, 22:53   #11
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...I'm just wondering about this from a CSI perspective. What would the forensics people look for in order to tell the detectives, "hey, your shooter used a 9mm (or 357SIG)."

First of all, CSI is total BS. The real answer would be:

"Sorry fellas, the lab is backed up for 6 mos. due to budget cuts. What's that? Rate of twist? Whadda we look like, NASA?"



If you want to know how murders are solved in the REAL World then watch The First 48. It's the most depressing show on TV as it really shows you how the other half "exists".
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Old 06-16-2012, 23:09   #12
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If you want to know how murders are solved in the REAL World then watch The First 48. It's the most depressing show on TV as it really shows you how the other half "exists".
The First 48 is one of my favorite shows, although it's true that it's very depressing.

Last night an episode featured three very young men (all teenagers, I believe) and two of them had no prior records of any kind. They decided to call another teenager for some marijuana and planned on murdering him beforehand.

The victim picked up a friend of his and both of them were murdered for a small amount of weed and $200. Not only are two young men dead for a piddling amount but three other young lives are completely down the drain. One has to wonder how some young people get so caught up in the gangsta image that they completely lose sight of reality.

It's astounding to me that a number of young people are without any moral compass or sense of values. More alarming is that we interact with a good many of them on any given day.
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Old 06-16-2012, 23:32   #13
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I doubt they could tell. I have been to a couple autopsies, spoken w/ the examniers. Unless you find something unique about the bullet, an expanded bullet isn't telling you much about the specifc case it was fired from. ACtual caliber is easy if enough bullet is left to measure, which cartridge was used, is almost always determined by finding a case.
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Old 06-18-2012, 16:30   #14
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You cannot tell for sure, but you could make some assumption. I think only Glock uses the faster rate for both 9mm and 357, or at least the number is low. I would say if the rifling has land and groves and has a fast rate of twist, it would be a 9mm. This all discounts after market barrels. BarSto uses 1 in 16 for their 9mm also. So if it had a slow twist, you would not know.
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Old 06-19-2012, 12:50   #15
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You cannot tell for sure, but you could make some assumption. I think only Glock uses the faster rate for both 9mm and 357, or at least the number is low. I would say if the rifling has land and groves and has a fast rate of twist, it would be a 9mm. This all discounts after market barrels. BarSto uses 1 in 16 for their 9mm also. So if it had a slow twist, you would not know.
I was wondering kind of the same thing with conversion barrels. like a 23 can use a 32 or a 9mm conversion barrel. I never figured how the would now a 23 was used to commit a crime if a 32 barrel was used.
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Old 06-19-2012, 13:28   #16
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I think this question only is relevant if you are a criminal. If it was a justified shoot and you had to go to court your gun would be evidence so they would know what you were shooting.
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Old 06-19-2012, 13:36   #17
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Originally Posted by Henry's Dad View Post
Here's a question that's been on my mind lately:

If a forensics team extracted a slug from a shooting victim, or a wall, or ballistic gelatin, etc., and the slug remained intact, how would they be able to tell if it came from a 9mm or a 357SIG firearm?


Sorry to say but, I think you have somewhat of a distorted view of what forensics actually says.

Absent some unique bullet style, a forensics report would read that the projectile in question recovered at the scene is approx. .355 in in diameter, weighing approx. 125, and a construction that would be consistent with ammunition manufactured by----(insert brand here),

The report would then indicate that rifling marks on the bullet revealed X number of rifling marks, right or left handed twist, conventional or polygonal bore.

The report would then conclude that the weapon in question is likely a (example) Glock type pistol of medium caliber consistent with a 9mm weapon, but also consistent with .357 Sig caliber and maybe even a .380 caliber (on the assumption that the bullet in question is a style loaded in both calibers).

The forensics reports you are citing exist...on television, not real life.

T.V. is great, I once watched CSI (Las Vegas) get finger prints off ......ready....a BRICK!

Let a real techno-weenie do that and they'll present him with a Ph.D..

Last edited by banger; 06-19-2012 at 19:38..
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Old 06-19-2012, 13:38   #18
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The projectile in a 357sig is not the same projectile as a 9mm parabellum. It's the shape and size of a .38 or .357magnum. The 9mm is ever-so-slightly narrower and has much more of a point.


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Old 06-19-2012, 13:45   #19
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The projectile in a 357sig is not the same projectile as a 9mm parabellum. It's the shape and size of a .38 or .357magnum. The 9mm is ever-so-slightly narrower and has much more of a point.


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