The knowledge of airline employees, of their own rules, is often hit or miss.
I have not had any trouble, but was flying to out-of-state shooting competitions, and every time, experiences with TSA and airlines provided interesting conversation over the weekend.
"Would you remove the firing pin?"
Would you know a firing pin if you saw it?
Over the PA: "I have a man with a gun."
TSA agent to me: "Did you know there was a dead rodent in your luggage?" He assured me he was kidding, and I wondered how funny it would have been if I'd replied, "Was the fuse still in it?"
The weight limit for ammo varies greatly among airlines.
A lot of plastic gun cases have a single hole for a lock, and the case can often be twisted enough to get the gun out; TSA will twist it to check.
I'd be VERY reluctant to pull the gun out at the ticket/baggage desk.
The tag that they give you goes in your luggage, but not in the gun case, so no reason to open the gun case before getting to TSA, where they will inspect the gun, but not in sight of everyone in the airport.