>>64046801
Seems that it's required in a lot of countries. I believe certain guns have to be proofed before sale if they weren't. There may also be a point a gun has to be re-proofed before sale but my euro gun laws are rusty. Even American guns get proofed in some countries; take my re-import 10/22 for example. British proofed.

>>64046891
>and how it was done (don't know if it's still done), is that any weapon for sale was sent to an independent proofing house, where they would prooftest the gun and then stamp it.
Countries like Britain would also mandate that any gun imported to the country had to be proofed, even if it was already proofed elsewhere
It's 5AM so maybe I'm misreading but unless things have changed since 1990-something, then yes they still have to be prooftested in the UK. See pic. Bolt, receiver, and barrel are marked.