+1 SouthWest....never had a problem. Delta placed my rifle on the wrong plane 2 years ago...had to wait for it to arrive the next day.
Hassle factor depends on the airport. Some will check your rifle curbside...KC airport for example.
Had a buddy recently who used a case with a combo lock and almost wasn't allowed to check it because he didn't have removable TSA locks.
I always pack ammo in the case with my rifle/shotgun.