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