From: "Jonathan M. Spencer" <jms@salvage.demon.co.uk>
Newsgroups: rec.guns
Subject: Re: polygonal barrels-can't be traced??
Date: 10 Apr 1998 23:23:11 -0400

In article <6flvrb$hvt@xring.cs.umd.edu>, Robert J. Christman
<rchristm@ix.netcom.com> writes

[snip]

#  Actually, comparing bullets from guns is pretty much a Hollywood thing.

Nope, it a real world thing.

#It
#can be done IF:
#1. the bullet is recoverd intact with no major deformation

On the contrary, all we require is a small area that matches.  An
expanding bullet helps preserves the tool marks we use.

#(pretty much requires
#ball ammo at low velocity)

Not so, I've matched military 5.56 bullets that are grossly deformed.

#2. the gun is found.  You wouldn't realisticly try to match all
#S&W .38 caliber
#guns in a city to a bullet.

No you wouldn't.  You would compare only supect guns to bullets

#Sometimes the type of gun can be determined by the type or rate of
#twist engraved in the bullet (assuming it is in good enough shape to do so).

It very often is.  We use not just the rate of twist but the number and
dimensions of the lands and grooves.

#Most rifles have sufficient power that the bullet will seldom be recovered,
#first it usually penetrates the target and goes on to hit something else, if
#that something else is hard the bullet may well be destroyed.  Secondly hunting
#bullets (most common in rifles) tend to come apart upon impact - this is what
#they are designed to do.  Handguns don't have the power of a rifle and even
#hollowpoints (assuming the work at all in a handgun incident) don't destroy
#themselves quite as thoroughly.

In fact, these latter mushroom and thus protect the vital land and
groove impressions.

#Shotguns obviously have NO ballistic signature on the shot, however a case left
#at the scene can, of course, be matched to the gun.

You are overlooking the wadding, especially plastic wads.  These can
often be matched to the barrel of a 'polychoke' gun or a sawn-off gun.

--Jonathan

Jonathan Spencer -- forensic firearms examiner
Keith Borer Consultants
Mountjoy Research Centre, Durham, England, DH1 3UR
tel: +44 191 386 6107   fax: +44 191 383 0686

From: "Jonathan M. Spencer" <jms@salvage.demon.co.uk>
Newsgroups: rec.guns
Subject: Re: polygonal barrels-can't be traced??
Date: 18 Apr 1998 12:42:32 -0400

The attributions might not be quite correct but it seems that:

In article <6gp32l$n5e@xring.cs.umd.edu>, Robert J. Christman
<rchristm@ix.netcom.com> wrote

taking exception to something I had written earlier

## In article <6flvrb$hvt@xring.cs.umd.edu>, Robert J. Christman
## <rchristm@ix.netcom.com> writes
##
## [snip]
##
## #  Actually, comparing bullets from guns is pretty much a Hollywood thing.
## #It
## #can be done IF:
## #1. the bullet is recoverd intact with no major deformation
## #(pretty much requires
## #ball ammo at low velocity)

and I said:

## Not so, I've matched military 5.56 bullets that are grossly deformed.

to which came the response:

#5.56 Military ammo IS ball ammo.  After penetrating a target it is usually at
#"low"
#velocity.

And I think there's been a little confusion.  So let me clarify.  Of
course military 5.56 is ball, no disagreement there.  And no
disagreement that high velocity hunting bullets tend to destroy
themselves (but that doesn't preclude finding a match, although one
would have to be lucky to find such).

Where I do disagree is the 'pretty much requires low velocity' bit.
Firstly, the 5.56 bullets in question weren't low velocity before they
hit the targets, and they weren't low velocity after they hit the
targets, either.  For that matter, they weren't low velocity after they
*exited* their targets.  They were low velocity once they struck the
earth and other material though.  The 'targets' in these cases were
humans, and light skinned motor vehicles (i.e. civilian cars).

I'm not suggesting that we can always find a match - far from it - but I
am saying that a match can sometimes be found even on high velocity FMJ
bullets that have gone through vehicle skins and then a human torso.

--Jonathan

Jonathan Spencer -- forensic firearms examiner
Keith Borer Consultants
Mountjoy Research Centre, Durham, England, DH1 3UR
tel: +44 191 386 6107   fax: +44 191 383 0686