Ballistics experts can’t testify that recovered bullets match firearms, Md. high court rules

[Biggfoot44]

Neutron activation is a very reliable way to see if the composition of a projectile is related to unspent ones recovered in the weapon or in the possession of the perp.

Although, in Baltimore, the thugs have defeated that by having every stinking round in a 30 round magazine scavenged from a different box (sometimes even different caliber) of ammunition. I guess modern problems require modern solutions.

I looked up the process to make sure . Neutron Analysis is extra precise technology to measure elemental compositions . But alas , it isn't probative .

Bullets are made in huge production lots . Hundreds of K at a time . And within the tons of a particular alloy mix , any slight variations in the mixing of lead , tin , and antimony will be randomly distributed . ( Cast bullets ? The vast majority of commercial cast bullets are made with the same 92/ 6/ 2 alloy , from a handfull of foundries . Also very popular with home casters .)

So at most . you could say that the bullet recovered from deceased Thug A was consistent with the bullets back at the crib of thug B .... And those of ten thousand other ammo owners in the state .

 

[Biggfoot44]

Just because I'm a curious person:

How many rounds need to be fired from a particular firearm between an evidence exemplar and a firearm test fire to make the comparison impossible? I'm assuming the microscopic marks left by the barrel on the projectile change far faster than the larger rifling scribe marks.

As we remember from the Fired Shell Casing Era , using state of the art equipment , with consecutive cases from same gun . had well below 50% matches .

Whatever degree there used to be with Uniqueness of Individual Guns is largely a historic relec of when quality guns were hand fitted , and cheap guns were crap .

In modern era of CNC and ISO manufacturing standards , guns are usually pretty darn uniform . At least until 100k of steel case Russian ammo chews up the extractor , or someone who compulsively overcleans after every firing puts a big nick in the crown .

 

[Blacksmith101]

This, ballistic comparison microscopy, seems to me to be something easily resolvable by properly controlled experiments. I’m more than a bit surprised that there is not a body of (forensic) scientific publications on just this topic. Surprising.

Here this link will get you started:

Internet Archive: Digital Library of Free & Borrowable Books, Movies, Music & Wayback Machine

archive.org

 

[DanGuy48]

Here this link will get you started:

Internet Archive: Digital Library of Free & Borrowable Books, Movies, Music & Wayback Machine

archive.org

Thanks, most of those look like methodology texts but might have had good references in the bibliographies if I were to spend the time going through them. I did another search in Google Scholar and came up with a couple research journal publications.

The error rate for both false positives and false negatives was under 3%. I’m surprised it isn’t better than that. Someone needs to develop a machine learning algorithm for this and I bet they could improve their accuracy dramatically.

https://onlinelibrary.wiley.com/doi/full/10.1111/1556-4029.15152

https://onlinelibrary.wiley.com/doi/abs/10.1111/1556-4029.14602

 

[ras_oscar]

This isn’t rocket science. If you bring me 3 pairs of cases fired from 3 different guns, I will sort them for you. The combination of firing pin, extractor and chamber scratches is very easy to match.

That's for the casing and likely useful for autoloaders. Revolvers allow the perp to take their brass with them (and dispose of properly i'm sure ) Which leaves the projectile

 

[Mark75H]

Good thing the bad guys don’t know

 

[BFMIN]

Unless the bullet is utterly smashed or fragmented I call B/S.
Rate of twist, number & dimensions of lands/grooves, direction of twist, minute bore imperfections matching engraving on the projectile & so on.
It may not prove bullet "A" was fired from firearm (2), but if its rifling engraved it wasn't a glock, if its a right hand twist it wasn't a Colt & so on can eliminate false positives.

 

[Mark75H]

Unless the bullet is utterly smashed or fragmented I call B/S.
Rate of twist, number & dimensions of lands/grooves, direction of twist, minute bore imperfections matching engraving on the projectile & so on.
It may not prove bullet "A" was fired from firearm (2), but if its rifling engraved it wasn't a glock, if its a right hand twist it wasn't a Colt & so on can eliminate false positives.

Correct, but only that far. If the bore had no significant imperfections, there is no narrowing down beyond make and model. The reason for the change is imperical evidence, many like bores present identical results. Skid marks from brand X tires of a certain size and tire line don't tell which car, only a car that could use that tire.

Exact height, shape, depth of firing pin dent, combined with extractor claw mark (differing by placement, wear and spring tension), ejector dent and possible case scratching or swelling from the chamber matches cases to a gun dramatically better than the striations left by the barrel and crown.

 

[BFMIN]

Agreed.

 

[coinboy]

Already disposed of. They were in the way.

Last I heard they weren't sure what to do with them and were considering giving to ATF.

 

[teratos]

Unless the bullet is utterly smashed or fragmented I call B/S.
Rate of twist, number & dimensions of lands/grooves, direction of twist, minute bore imperfections matching engraving on the projectile & so on.
It may not prove bullet "A" was fired from firearm (2), but if its rifling engraved it wasn't a glock, if its a right hand twist it wasn't a Colt & so on can eliminate false positives.

At crime scenes EVERYTHING is fired from a Glock….