Seriously: As for altering the fingerprint, I suggested a while ago that a coded pattern be engraved on the lands that would carry a digital ID. With code redundancy and error checking, it is possible that clumsier attempts to alter it or even the degradation from normal wear and tear might not destroy enough of the pattern to make it unreadable.
For such weapons as Saturday Night Specials, they're probably used seldom enough, and are cheap enough to not make it worth the bother of altering them.
And the more sophisticated attempts might not be able to forge a different code, so at least the tamper would be evident. But most criminals wouldn't even bother; they're not always people of means or ability, and often the crime is a crime of passion. In such cases, every little bit would help. It's not necessary for something to be 100% foolproof in order to be useful.
I think it's a good idea, but to be effective, we'd need better records of legal gun transactions as well, and _this_ is what the nunguts are really upset about; they don't want the gummint knowing who has what guns, for some reason. Reasonable people don't mind having VINs on vehicles to identify them, registering their vehicles, and informing the gummint about sales, and this _obviously_ helps in tracking stolen vehicles, and in finding out who might have used a vehicle spotted in a crime. You'd think the same would be true of gun owners, but the nunguts have this idea that the gummint is someday going to come and take them away, and that then they'll have no defence against the gummint. . . .