AS had been mentioned, TSA locks are for the suitcase, NOT the gun hard case inside the suitcase.
I travel with my pistols at least 2 weeks a month to my job in another state. I carry 2 glocks(23C & 35) 2 boxes of ammo plus mags.
These are in a small Pelican case. That case is locked with 2 high end Master Locks with medium long shanks.
I Then take a high end Master cable lock, unzip the suitcase liner and run the cable lock under/behind the stowable metal drag handles, then before I close the Master Locks on the Pelican case, I run the cable through those and then lock the cable.
Then lock the lock on the case. That way the box is locked and its all cabled locked to the suitcase. Not fool proof but a MAJOR deterrent to anyone trying to get the weapons short of taking the whole large suitcase.
After I delcare at the ticket counter(and no they dont ask to see the weapon, but will ask if the ammo is in the original mfg box. You cant NOT have any magizines loaded!!!!!)
I fill out paperwork, then head to the TSA special bagage inpsection station with the ticket agent(once TSA is done with the bag, the ticket agent must control it from that point until its loaded in the TSA baggage CTX machine for Xray). Sometime they will just open the suitcase and wipe the weapon case for residue, once clear, they will lock using your TSA luggage lock.
At this point I also put a small ziptie through the zippers where the TSA lock is placed. This way once the bag arrives at the destination baggage carrousel, i can instantly tell if the suitcase has been opened.
Sometimes at the TSA special baggage check they have taken 35 minutes opening/inspecting everything in that bag.
I usually carry my IFAK, Suture kit, extended medical kit, large dropped legged combat knife, mess kit, MSR Wisperlight Stove/bottle(no fuel) water filter/pump, fire making kit and misc survival stuff.
They have opened and emptied each of these thing above. I stopped them from taking apart the North American Rescue TORK (IFAK)kit. They started to take out and open the chest decompression needle and I exploded. I said for $300 you can open anything in that kit, cuz once you break the sterile seal, you own it. They got the message.