From: "Jonathan M. Spencer" <jms@salvage.demon.co.uk>
Newsgroups: rec.guns
Subject: FORENSIC needed .22 info for trial
Date: 10 Feb 1998 20:33:26 -0500

In article <6bd5r2$aan@xring.cs.umd.edu>, Gregory Prior
<prior@televar.com> writes

[snip]

#A couple of years back I attended a very interesting lecture by a renowned
#forensic chemist, a portion of which dealt with "powder residue".  According
#to this gentleman, there is virtually no way to trace "powder residue" from
#a rim fire .22 because the traceable elements come from the primer, not the
#powder, and are nonexistent in a .22 rim fire.  Therefore, trying to get a
#residue test on a shooter's hands or clothing when the gun was a .22 rim
#fire is a complete waste of time for the officers and the lab.

It's true that a .22 rimfire uses just 1 grain or slightly more of
propellent, but that doesn't mean there's no point in looking for
residues.

The residue that is looked for from propellent is nitroglycerine, which
is detectable down to one nanogram -- one **thousand millionth** of a
gram.  Therefore, the labs can (and do) find even the tiniest amount.
However, unless the propellent in question contains NG the lab isn't
going to find any.  (Obvious, but sometimes the obvious needs stating.)

That said, the residues are easily removed through physical action.  A
good shaking of a garment will remove many particles of residue, and a
good washing of the hands will clean them.  The actual residues, once
formed, are very stable though.  And the labs can detect quantities that
are so small are to almost defy human comprehension.

The amount of priming compound in any cartridge is very small -- I
measured the quantity in some IMI .45ACP cases for a well publicised
trial last year, for example, and it was something like 0.1 gram.  I
don't know how much is used in 22 rimfires never having scraped the
stuff out, but it isn't going to be more than the 45ACP.  :-)

Often, when looking for primer residues, a scanning electron microscope
is used to look for characteristically shaped particles of lead, barium,
and antimony (all three elements together, not just one or two or them).
But other methods can be used.  For example, the IMI 45ACP primers
contain the high explosive PETN and this can be detected but by other
methods.  In the case I mentioned above, the defendant was accused of
planting a bomb and some PETN was detected on him or his clothes (not
sure which now).  We were asked: could that PETN have come from the IMI
ammunition he'd been legitimately using?

--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