I have travelled with firearms in many USA states and used a non-TSA lock on my gun case without issues. Sometimes (Cali) The TSA agents literally dumped everything in my case out and searched under the foam for "Contraband".
Travelling to/from African I used two TSA locks on my gun case and one on my ammo case. In only one instance I had TSA request that I add two more locks for a total of four onto my gun case. I was told that this was because the case had four locking points and thus required four locks.
This year when returning to Africa via the same airport, same gate, using the same gun case, I once more applied only two locks and it was approved coming and going without issue. When travelling domestically 2021 with a rifle and ammo from KY to Cali and back, I locked the ammo and the rifle in the same case. Obviously that is not allowed going to/from Africa. I have found that every airport seems to have practices that differ from the next which implies a lack of training and/or lack of TSA agent professionalism. Not exactly the cream of the crop. Some agents did not want to see the guns, let alone allow me to open the case. When I arrived in California once for a rifle match, I received my gun case at the baggage claim point and asked if I could open the case in front of the agent to inspect my rifle to confirm that it arrived intact and undamaged and was told emphatically that I was NOT to unlock the case until I was outside the terminal on the sidewalk.
I was not at all happy about that since I felt much safer inside the terminal. They are a wonky bunch. You would have thought that I wanted to open a case full of Monkey Pox or Nuclear fissile material.