Originally Posted by
Peter Laidler
A forensic chap told me that if the original number had been pressed or rolled in place and then it's been filed/ground off, the original number can usually be identified by the impressed striations left behind when subject to forensic testing (don't ask me how............)
However, if the number has been CUT - as in engraved, then it is usually lost for ever by filing/grinding.
We have an ex IRA Thompson gun No 480 that has had the number ground out. Forensically it was raised to read 482........ the remaining striations of the 0 being misread for a 2. But not bad!