I think one point you have missed is that the Proof House here in Britain is nothing to do with the Government; they didn't set it up, it was the Gunmakers themselves in order to protect their products and the public from poorly made guns being sold.
There are comparable organizations already existing in the US. Underwriters Laboratory is one - I believe they provide some industry standards and testing on various products. ASTM is another - they set standards for a wide range of industries but I don't believe they actually test products. The underground storage tank industry had the Steel Tank Institute - not sure if it still around, but it set manufacturing standards for USTs and then offered insurance against tank failure for its members covering tanks built to those standards.
These organization do not have governmental regulatory authority, but in some instances the government mandates compliance with their standards. I think that is how it works in the UK - the proof house sets the proof standard and the government mandates that all guns sold be in proof.
