A lot of people who don't want to lie (which may not be illegal, but I wouldn't recommend it personally) will get a starter pistol. They're cheap, small, safe (don't fire rounds, just blanks) and legally have to be declared as a firearm to fly. So you buy a starter pistol and stick it with your nice camera when you fly. It will be locked with something only you can open and will probably be handled more carefully in transit

I doubt it, but sometimes counter agents will want to see that (your real firearm) is unloaded and stowed in the proper kind of case (hard-sided - I use a very large Pelican).

More often than not, the TSA will want to hand-inspect firearm-containing baggage (with you present), and I couldn't say what they'd do if they didn't find the firearm in the bag they were breaking their routine to check.

Just buy a flare gun or a starter pistol and declare it if you don't want to or can't use the real thing.

no