At SEA, the ticketing agent didn't even check to see if the weapon was in the proper unloaded state, just asked me if it was, had me sign a tag and told me to walk it down to the TSA inspection station. The TSA clerk put down his book, barely glanced at me, didn't even look inside the suitcase, and put it on the belt.
The whole process was much less hassle than I was expecting from the TSA.