I've had great experiences on American Airlines over the last 7 years flying multiple times a year. Pistol locked in a lunchbox sized Pelican case, clerks always just had me sign the unloaded form and set it on top of the Pelican, then wheel it over to TSA at the DFW airport, or more often at other airports they just put it on the conveyor and had me hang out for 10 minutes to make sure it cleared TSA.
Southwest was a little odd at Love Field a week ago - the ticketing agent had me open the slide to demonstrate it was unloaded. That was more reminiscent of when I used to fly with firearms around 1999-2002. On the way back to Dallas from Tucson, the ticketing agent looked horrified that the Dallas agent had had me do that, and indicated that he must not be briefed on current procedures because that's no longer their procedure.
Over the last 10 years of flying with firearms in checked baggage, it really is usually a pain-free, easy process and I've had no real troubles.
Glock 17, 26
Walther P99c QA
Sig P2340 (.357)