Due to a previous job that required me to throw a proverbial dart at a US map and travel there on short notice I have flown with firearms hundreds of times. By my count to 40 plus states give or take a few. I have been through many of the airports mentioned in this thread. My last set of flights were last July, fortunately that was for a well needed vacation.
I have never used a TSA lock. I always used regular keyed pad lock. I have never been asked to by an airline or TSA agent to use a TSA lock. I have never had a lock cut on any of my gun cases.
About 98% of the time I was just raveling with .45 for personal protection but I would haul out long rifle cases when traveling for a hunt. I always use soft sided luggage and put my .45 in a hard-sided case inside the luggage. I fill out the declaration tag and drop it in the hard-sided case then lock it up, usually with the airline agent watching, then zip it up and they take it. I never put locks on the outside of my luggage.
Normal procedure is to wait in the area to give TSA time to receive your bag and be able to call you to come unlock it if they choose to physically inspect the case firearm ect… That varies by airport some, but the basic procedure is the same. I always arrive a couple of hours early for a flight, since 9/11 anyway, so I don’t care if they take extra time for inspection.
I have not been asked to take a firearm out for inspection to insure it is unloaded in well over a decade. That stupidity seems to have stopped. I would refuse now with out an officer or TSA agent because I don’t want to get shot (as mentioned previously in this thread).
I have been asked about ammo on occasion, maybe three out of four times but I never carry more then 50 rounds, usually only 24rds for three mags so I never come close to the max on ammo. Please note the specific airline policy on quantity of ammo allowed before flying. In my exp the airlines have different policies covering that regardless of TSA max allowed. Best not to be arguing what the TSA rule is with an inexperience ticket counter agent who only knows airline policy if that. If you need a lot of ammo where you are going ship it in advance.
What was new on my last set of flights was in two airports they took my locked case and tried to pull it apart with the lock on and see if they could still stick their hand in. I had foolishly used the gun case my new S&W M&P .40 came in with a pad lock on it. Never again. Case was too flimsy but after a short discussion with the lead TSA agent that had been called, he approved it for travel. I told him thank you and that I would never travel with that case again. Get a Pelican 1170 and don’t look back.
One last thing. I refuse to ever travel through NY airports or Logan ever again. Google what can happen if you try and check your firearm at one of those airports or pick one up after landing there.
There for what it’s worth in my experience flying with firearms in the US.
HTH