I also can't stand poor grammar. If you notice, journalists used to be held to a certain standard ... not anymore. You'll see them use improper tenses all the time. It's as if the word 'proven' no longer exists.

Just like the morons who drink 'Sweet Tea'. Aside from being bilge water, it is 'Sweetened Tea'.

Anyway, I believe that the rules are a little different when it comes to what is really a set of technical terms. While you would never say 'those facts have been proofed' I think it is probably correct to say 'that gun has been proofed'. It's probably also correct to say 'proved'. but I am sure it's not correct to say 'proven'.

As near example is the hanged/hung bit - onc your clothes have been put up to dry, they are hung but once your Uncle Ned is swinging from a rope he has been hanged.