I have flown Northwest for the past six years with guns (Boston through Minneapolis into Bozeman Montana). I've always arrived early and never had a "chip on my shoulder" (although travelling to airports with guns isn't fun) and have never had a problem. I've been lucky because all the ticket counter folks I dealt with have been great.

From my experience with Northwest, 2 guns max. in one case, ammo separate (I put it in with checked luggage, tell them at counter, and they'll make you open the bags to verify). Eleven pounds max. weight allowed for ammo (I got it checked of all places in the Bozeman airport where I would have thought the agents were used to seeing guns/ammo in the fall. I told agent I had two boxes of centerfire ammo which weighed at most 1.5 lbs each - but they weighed them anyway). Other than that, no problems with airline and personnel.