My High Standard was doing the same thing, and I tried some of the things your gunsmith tried.
Then I ordered a new firing pin and spring......
I just installed a new firing pin in my High Standard today and test fired it (dry fired) with a spent .22 case and after 2 strikes of the pin, It was blunted so badly that it was hard to tell if it hit the case.
The pin went back to Numerich parts return today.
I never intentionally dry fire a rimfire, but have had several failure to feeds that result in dry firing, But that new pin only hit brass and it deformed the tip.
They have some issues with their metallurgy. IMHO
I will post any new developments.
For the message of the Cross is foolishness to those who are perishing, But to us who are being saved, It Is The Power Of God. 1Corinthians 1-18