Just a historical question for our US cousins:

Proof testing & marking of firearms seems such an obvious precaution that it has been law across most of Europe and Russiaicon since the 17th/18th centuries - I'd guess it must be one of the oldest forms of government quality certification still going. Most countries also made certification of the firearms the legal liability of the vendor.

How is it that the US - especially with its huge firearms market - never introduced either a federal compulsory testing regime or specific liability to gun dealers? Early US administrations quickly copied virtually all other aspects of government controls, so it seems strange that firearms proof wasn't included. It doesn't even seem to be an issue of State or personal freedom - the common-sense need for proof has never been contentious in any kind of society across the rest of the world.