Our local TV station last night (www.wfaa.com) ran a piece where there was a proposal before congress to require all guns to be fired with a sample round prior to sale.

These sample rounds are then kept by the manufacturer, as the striations on the bullet created during the firing appear to be as unique as fingerprints under a microscope.
I don't know about all guns sold in the US, but when I bought my Glock earlier this year (Glock 35 - .40 caliber semi), I received the casings from 2 rounds that were put through the gun by Glock before it was shipped to my gun shop.

According to my father (who is much more into guns than I am), at least one casing was also sent to some national database. And the test-firing/casings-sent-to-national-database thing is a recent federal law, in place for all handguns sold in the US.
However, one key point was made. If someone wanted to beat this system, they would merely need to "alter" the rifling in the barrel slightly by scratching to create a different signature than the one left with the manufacturer.
Or replace the barrel completely. This isn't that hard to do, either. Nor is it illegal.
How about revising the the Constitution's prohibition on "cruel and unusual punishment" to read more like "punishment which is appropriate in severity and administration to the crime committed"?
I disagree with this. I personally think the Constitution (as far as this topic is concerned) is fine as it is.
Punish criminals, not gun owners. And don't make gun owners into criminals.
Amen.