i flew northwestern a while back and had a hassle free trip. I called ahead and asked what their rules were and what I needed to do before checking in. I pulled the bolt, had the ammo in a seperate, locked container, and had my serial numbers written down ahead of time (they didn't ask for them). I had to fill out a short form at the desk and put it in the case.
my advice: call ahead and ask what they're policy is... my trip was extremely hassle-free