Big red flag!!!!
Your "gunsmith" told you the hammer won't cock when the grip safety is depressed, and it's supposed to work that way?
And you believed him?
Think about it for a moment, IF what that idiot said was true, how could the gun even fire? The gun doesn't know if you are cycling the slide by hand, or if its being cycled by firing. You have the grip safety depressed when you fire the gun, and the slide cycles, leaving the hammer cocked.
Your "gunsmith" is an idiot, did not do his job correctly, and LIED to you to cover it up! DO NOT DO ANY MORE BUSINESS WITH THIS GUNSMITH!
He may know lots of other guns well, inside and out, but rather than admit he didn't know this one (admit its kind of rare, and he would have to learn it), he blundered ahead, and then lied to you about how it's "supposed to work".
Proven untrustworthy. Sorry.
Find someone else, even if you have to drive for hours. Since he screwed up on this one, and lied about it, can you trust him NOT to screw up on something else? I wouldn't.
All else being equal (and it almost never is) bigger bullets tend to work better.