From: jim bell <jimbell@pacifier.com>
Date: Mon, 5 Aug 1996 03:12:20 +0800
To: Sandy Sandfort <dlv@bwalk.dm.com>
Subject: Re: Stop the presses -- Anti-terrorism bill not that bad
Message-ID: <199608041735.KAA21449@mail.pacifier.com>
MIME-Version: 1.0
Content-Type: text/plain


At 08:37 AM 8/4/96 -0700, Sandy Sandfort wrote:

>
>On Sun, 4 Aug 1996, Dr.Dimitri Vulis KOTM asked:
>
>> Is there truth to the rumor that poking a file inside the barrel
>> will alter the marks on future test firings?

>I have heard, but have not evidence for, is that with use, these
>characteristic markings change.  As a result, putting 200-300
>rounds through a gun at the range is enough to alter its
>identifiable barrel markings sufficiently to defeat forensic
>matching.  Don't know, just heard, but it sounds reasonable.

Heard same thing here; it's almost certainly true.  It would help if the gun 
got a thorough cleaning as well:  You can "de-copper" a barrel by plugging 
one end, and filling the barrel with an ammonia solution. (this is available 
as a commercial product for guns, at wildly-inflated prices.  Ordinary 
ammonia solution works just as well, cheap.)   This dissolves the copper 
left from the passage of copper/brass-jacketed bullets.  You can tell it's 
working:  The copper forms the distinctive blue cupramine ion in solution.


BTW, all this changes is the microstructure of the markings:  The number of 
riflings and the twist of the riflings are, obviously, unchanged.



Jim Bell
jimbell@pacifier.com