Please explain how mass produced guns result in unique markers qualifying as evidence of crimes in the court of law. It seems like it would not warrant the validity it is given in court with all the manufacturing quality control measures, etc. TY
In: Engineering
Identifying caliber and rifling rate is useful, without anything else.
Beyond that, mass production is designed to be exactly as inconsistent as possible while still working. This is a cost saving measure. This means that no two items are the same. On top of that, wear and tear from something as tiny as a sand grain can leave recognizable permanent marks in a gun.
Lastly, they use some wild shit in court. It is not as high of an evidentiary standard as you might like to think.
No barrel is perfectly smooth. Every barrel has small imperfections – cuts, grooves and bumps. When a bullet is forced through the barrel at high speed, these imperfections cause the bullet to have a fairly unique “imprint”. These may be sufficiently unique to give a strong indication that a bullet was fired from a particular weapon. It is not an “evidence of crime”, it is “evidence that this bullet was fired from this gun”.
It doesn’t. It’s mostly junk science that prosecutors have convinced judges is real and is propped up by crime drama TV shows like Law and Order or CSI. AT best, you can reliably identify things like caliber size and characteristics of the barrel groove, which can tell you gun make and model but that’s about it. There *might* be some unique wear patterns in the barrel, extractor, or ejector, and those can leave markings on the bullet or the casing, but that’s a big if. It also requires having the bullet or casing and the specific gun in question to match the markings to.
Gun barrel is a metal tube that’s supposed to handle rapid expansions of gasses (aka contained explosions) and a steel-jacketed metal object (aka bullet) clawing it’s way out with insane friction, and with rifling, even moreso. And for automatic weapons, that’s supposed to happen hundreds of times per minute.
This causes a lot of damage to the barrel (and the bullet), which makes it quite distinct.
As if it’s really unique and legally airtight, is unlikely. More likely is that it provides good amount of proof supporting rest of the case/proof/witness statements/etc, not make a case entirely by itself.
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