alt Hacker NewsFor most modern guns, it would be the firing pin, also called the "striker". Nobody manufactures microstamped guns, but if they did, the striker is a $20 part you can replace in ten minutes - or you could just spend half an hour on target practice at your local range, because 200 rounds are apparently enough to wear the etching down to illegibility.
They know this, and they know the technology just isn't there. But that's their goal - to make gun ownership as difficult and expensive as possible.
I think they've learned from the anti-gun lobbyists and are now pushing to end anonymity on the internet the same way.