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Subject: FORENSIC what does a firearms examiner *do*? (long)
From: "Jonathan M. Spencer" <>
Date: Jan 09 1997
Newsgroups: rec.guns

I keep getting asked: 'what does a forensic firearms examiner actually
*do*?'.  Well, here's a partial answer.

'Forensic' means 'for the courts'.  So a forensic scientist is a
scientist who works for the Courts.  Since the prosecuting authorities
make use of the Home Office, Northern Ireland, and Scottish laboratories
- and I am independant - it follows that most of my work is in advising
defence lawyers.  That may be become apparent in what follows.  But
there is some civil work, too.  My work is not limited to these shores:
I have advised in several foreign countries too.

A firearms examiner will typically be engaged examining firearms,
ammunition, components, tools etc that have been seized by the police as
evidence of some crime.  This might require the examiner to identify and
classify (according to the law) recovered firearms, ammunition etc.
This is much more than merely saying 'this is a Browning High-Power'.
For example, does it function; is it therefore a lethal barrelled weapon
and if so, is it under English law a 'firearm'?  (A test-case in the
Scottish Court of Appeal heald that a revolver that was not capable of
being fired, due to a mechanical failure which required repair, was not
a 'firearm' since it was not *presently* capable of causing a lethal
injury.  Hence the appellant was innocent of the crime for which he had
been convicted.)

In one of my cases, a nasty murder in which a shotgun was fired into the
skull from inches away, a length of tubing was found in a ditch many
miles from the scene.  The Home Office scientist involved claimed that
it was from a little-known single-barrelled French shotgun.  He had done
a sterling job, and was right.  He obtained a sample of the gun from
France - the only one ever to have been sold to Britain.  He had
measured all the dimensions, including even the fine bevel finish on the
outer edge of the muzzle and obtained a perfect match.

He took cuttings (chippings) from the new shotgun barrel and from the
sawn off suspect 'tube' and subjected them to an elemental analysis.
(I'm not sure which technique he used.)  He did the same for some metal
chippings recovered from a hacksaw found in the accused's house, and
more metal chippings vacuumed from the carpet in the accused's house.
They all matched.  (I later obtained from the barrel manufacturer the
elemental composition of the barrel: it matched the suspect tube and
chippings.)  The shot recovered from the deceased's head matched that in
the ammunition which had the unusual plaswads - but it also matched most
shotgun shot, being lead:antimony alloy.

He took the plastic wad (recovered during the p.m.) and measured the
degree of 'flare' on the bottom cup.  He uniquely identified the plaswad
(an unusual type) and obtained a sample of the same ammunition (trap
ammunition).  He test fired the ammo in various sawn off shotguns held
at the laboratory and obtained a variety of flared cups.  Through this
means, he was able to say that the crime plaswad had been fired from a
shotgun with a barrel length of 'x'.  When he took the dimension 'x' and
added to it the length 'y' of the suspect tube, it equalled the original
length of the French shotgun's barrel.  The evidence was adding up.  All
four defendants were convicted of murder.

A regular question I have to consider is whether a given air rifle is a
firearm?  Well, is it a lethal barrelled weapon capable of discharging a
bullet, shot or other missile?  And what is meant by 'lethal' barrelled?
This leads us to test fire air rifles to try and determine whether they
could kill.  10ft-lbs of muzzle energy, and possibly less, has been
known to kill.  Under English law, air rifles that exceed 12ft-lbs are
classed as 'especially dangerous' and they are subject to licensing the
same as regular rifles and handguns.  We deal with many injuries
resulting from the abuse (generally, by youths) of air rifles.  Oddly,
the loss of an eye seems to be one of the most frequent forms of injury.
(The fools seem to aim for the head.)  Many times the pellet is lodged
behind the eye and, if the eye still functions, the surgeon refuses to
recover the pellet.  Hence a prime piece of evidence is missing.  We
once had a case where it was alleged that a .177 pellet had been
discharged in a .22 rifle.  The pellet remained inside the injured
party's head and, in its absence, it could not be demonstrated to the
Court's satisfaction that the pellet had been fired by that gun.  An
acquittal resulted.

Air rifles, in the hands of adolescents, are seldom quality items nor
are they cared for.  Several times I have tested air rifles seized by
the police to determine whether they are prone to 'accidental discharge'
(negligent discharge if you prefer).  Frequently, they are since the
sears are worn and rounded.  On one occasion, I examined an air rifle on
behalf of a plaintiff (i.e. he was sueing someone.)  This air rifle had
been incorrectly assembled and over greased by an incompetant gun dealer
(after changing the mainspring) and it fired just as the owner was
placing a pellet into the breach through the loading port.  The sliding
cover shot forwards and amputated half of his finger.  So it isn't all
criminal work, only about 98% of it is.  :-)

Another question, which relates to classifying guns, is that of antique
firearms.  Under English law, an 'antique firearm' which is held as an
ornament or a curiosity, does not require a licence.  But what makes a
firearm an antique?  Well, it doesn't have to be 100 years old.  The
Courts have repeatedly rejected this test, determining that a 1908 rifle
in one case *was* an antique.  I tend to consider the question: is it a
relic of times past?  I have, successfully argued, that a revolver of an
old design, that is chambered for an obsolete (but still available)
cartridge, and proofed only for black powder, is an antique firearm even
though it is porbably under 100 years of age.  On the other hand, I have
also advised that an old style hammer gun (ie shotgun), proofed for
black powder and nitro-powder between 1904 and 1925, ought not be
considered an antique firearm on the grounds that the damage done to it
(sawn in half lengthways and then re-brazed together) would preclude
anyone from using it as an ornament, and that it would be of no interest
to a genuine collector.

Quite often cartridge cases and bullets are recovered during crime scene
examinations (or post mortems).  As many folks are no doubt aware, many
barrels (including shotgun barrels) leave unique identifying marks on
their projectiles.  To establish whether a given firearm fired a given
projectile, we examine the projectile under a high quality microscope
(but not necessarily high magnification) to find 'toolmarks' that might
be unique to that barrel.  (Most barrels do produce unique toolmarks.)
We then fire 'control samples' in the suspect weapon to produce fired
projectiles for comparison against the crime projectile under a
'comparison microscope'.

Sometimes, especially if the crime projectile is damaged (and they
frequently are) much of the original toolmarkings are distorted or
destroyed.  We may need to fire several control samples, using different
brands of ammunition, to produce a good sample for comparison.  I have
been known to fire more than 30 shots before obtaining a match - but
when that match is obtained, there's no walking away from it.  If the
crime projectile has good toolsmarkings, it doesn't require a great deal
to form a positive opinion.  I have made a positive match on a concrete
impact damaged FMJ 9mm bullet (that had already gone right through a
human skull before meeting the concrete) on which was about 3mm of
undamaged rifling: fortunately the gun (a Browning 1935) was very

Similar comparisons can be made on cartridge cases using the chamber's
wall markings, firing pin marks, extractor and ejector markings.  This
field is known as 'firearms identification'.  I recently had a Star
Model B 9mmPara pistol which was so loose that the 'dynamic marks'
caused by the barrel & slide moving reletive to one another was so much
that the fired cartridge showed no firing pin impression whatsoever.
(But was a piece of cake to match on the dynamic marks.)

Lawyers know a lot about the law, but most of them know little about
guns.  So my reports typically contain some 'background' information
explaining how a revolver works, or how a self-loading pistol ejects it
empties, or the theory of patterning shotguns, and so forth.  In Court,
I have to assume that the Jury know nothing about guns and so elementary
explanations on operating principles are required.  But just to be on
the safe side, I'm always remind myself that among the twelve there may
well be one who knows more than I on the subject! :-)

External ballistics, and terminal ballistics, are a common item.  This
ranges (pun intended) from calculating a trajectory and terminal energy
for an airgun pellet to assessing the spread of shot at the point of
impact and estimating the muzzle to target distance.  (This latter
usually involving a sawn-off shotgun and a human torso.)

On one occasion, we were supplied with a time-lapse video recording of
an object, alleged to be a pound of mince beef impregnated with slug
pellets (the poisonous variety), flying across camera and into a dog's
kennel.  We were provided with a map of the house in which the camera
was situated, and of the neighbouring houses and grounds, and were asked
to calculate the origin of the projectile, described by the lawyers as a
'meat pie'.  This become known as 'the flying pork pie case'.  We were
able to calculate, to within an acceptable margin of error, that the
meat pie most probably originated from the bedroom window next to the
one with the camera, and was most unlikely to have come from the
neighbouring property.  In other words, the dog's owner (who was the
only person who knew the camera was present) threw the object himself.
The defendant was acquitted in that case (rightly so IMO).

Firearms discharge residues (FDR) are another regular.  Although I cam
not a chemist, I am asked to provide opinion on the behaviour of the
materials discharged when a firearm is fired (e.g. the smoke etc that is
discharged when a shotgun is fired through a house door inside the
house).  The residues that concern us consist of lead, barium, and
mercury (from the primer), lead and copper (from the bullet), and
nytroglycerine (from the propellant).  Extremely sensitive tests exist
that can detect down to 0.1 nanogram (yes, nanogram) of nitroglycerine.
Of course, not all propellants use the stuff and if it ain't there, it
can't be detected.  But if NG is detected at the crime say, from a
swabbing of a cartridge case or a wound swab, then the suspect and his
clothing should be tested to demonstrate an association with the scene.
Depending upon the circumstances, a negative result for NG (or the other
FDRs) may be strong supporting evidence that a person was not involved.
Or it may be fairly neutral evidence.  However, finding lead, barium,
and mercury (of the right sort in the right quantities) would be strong
evidence that the suspect had been near a gun when it was fired.

This week, I have been working on a case where the injured party, I
refrain from using the word 'victim' because often they are not entirely
innocent parties, has an odd wound to the forehead.  It is alleged that
this wound resulted from a .25ACP pistol being held in 'hard contact'
against the forehead and being fired, but when the bullet failed to exit
the barrel, some hot gases by-passed the bullet and seared the skin.
The wound is atypical of a contact wound.  No gun has been recovered,
but four old tarnished unfired .25ACP factory loaded cartridges were
found at the scene.  From this, the assumption has been made that a
.25ACP pistol was involved.  But no fired cases were found and at least
two shots are alleged to have been fired.  The cartridges found have not
recently been in a magazine nor have they been chambered.  There is
light soil in the primer pocket (so they may have been on the ground for
a while and pre-date the incident).  The wound was not caused by a
bullet (at least, not a normally discharged bullet) and, of course, no
swabs were taken from the wound or surrounding area for FDR analysis.
So there is no concrete evidence that a gun was even discharged - just
what the witnesses allege.

I have a case where a gamekeeper shot a domestic cat using a 12 guage
shotgun but did not kill it (it ran off).  He fired 1 1/8 ounces of
English no 7 shot (making 383 pellets in the cartridge if memory serves
me), and 45 pellets were observed in the cat's head at x-ray.  He is
charged with 'causing unnecessary cruelty'  which requires the element
of intent.  He claims it was an accident: he fired at a rabbit a few
yards from its hole, and the cat leapt up and ran off.  There is a
witness (next door neighbour and good friend to the cat's owner, and a
cat owner herself) who claims to have seen him shoot the cat
'deliberately'.  (Her statement made three weeks after the event.)

An examination of the scene revealed that there are rabbits' holes where
he says he shot at; that he may not have seen the cat in the (then) long
grass; but more importantly, that he was not visible to the witness who
claims to have seen him from where she says she was.  Hence her evidence
is false.

Test firing his shotgun (at proper patterning targets - available from
the NRA and just the ticket for the job) reveals that his gun shoots
about a foot high and left at the relevant distance.  All of which is
valuable to his lawyers to try and persuade the Magistrates that his
intent cannot be demonstrated beyond reasonable doubt - and so they
should acquit him.  Fortunately, it is not for me to determine who is
telling the truth and who is lying.  :-)

An interesting experiment I undertook some long time ago involved firing
00 Buckshot through double glazed windows to determine how the pattern
(spread) alters under these circumstances.  (It opens up dramatically.)
More recently, I was required to discharge .22 rimfire ammunition using
a pair of pliers and a hammer to evaluate the 'external' ballistics of
the bullets.  We've tested the terminal ballistics of a wide variety of
air rifle pellets by using pig's heads, and large joints of pork,
including 'dressing' the pork in a pair of trousers to catch the imprint
of the cloth on the pellet's nose.  (It works.)

Well, there's a snapshot of the kind of work undertaken by a firearms
examiner.  That was what came to mind just now.  If I check my database
of cases I might turn up some of the more unusual work and, if it looks
likely to be of interest and not _sub judice_, I'll post it.  I haven't
mentioned the man making sub-machine guns (by the hundred) in his
garage; nor the man who had two bullets inside him but only one entry
wound; nor the home made zip guns.  Give me time.

If you email me in response to this posting, don't expect a quick reply
because I'm going to be away for a week or so.

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

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