One thing that is guaranteed is that nothing is guaranteed. Every airport and person will be different. I flew to Idaho for a trip this fall with a double SKB case and masterlocks. I used some miles to upgrade to first class so that I could take advantage of the extra baggage and priority stickers. While waiting in line for the 1st class counter, I noticed the woman in front of me was rebooking a flight and taking forever. I should have paid more attention. When it came to be my turn, the check-in agent at my origination airport said that I had to give her the key and she had to take the case behind the counter to the TSA area where they would inspect. I argued a bit, but she said I couldn't go back there. She made me open the case right there at the check-in counter, put a firearms declaration in there and close it up and relock it. She took it back to the TSA agent, and brought it back out almost immediately and he had told her if she had already inspected it, he didn't need to. This all confused me and I just took the baggage claim stickers, waved good-bye to $5k+ worth of gear, optics, and my rifle, and boarded my flight.
I get to BOI and there were a dozen or so active duty troops with me on the plane they were picking up the exact same rifle case as I had at the baggage claim. I waited for my luggage and rifle case ... nothing. I asked the luggage claim agent, she said everything from the plane was unloaded. She asked for my luggage claim tags and that's when I noticed what had happened. The woman in front of me didn't check luggage, but they had printed luggage tags for her and put them on my bags and sent them to (maybe SFO). Here's where it gets fun. Because she didn't check bags, there was no passenger to assign the tags to when they scan them onto the plane. Because my tags were never used, there was nothing assigned to me in the system, so it was showing my bags still at my origin. They were essentially free-floating in the system. I filed a report, and gave them descriptions.
Fortunately, I put my name and phone number on the outside of my rifle case. GOod idea, bad idea, I don't know (it has it's pros and cons), but I got a call the next day from the SFO baggage office and they had my case. He said he could get it on the next flight to BOI that afternoon, but I would either have to send them my key to the locks, or they would have to cut them so the TSA could inspect it. I thought this kind of defeated the whole idea of no one opening the case except me, but I wanted my gear. I told them to clip the locks and they replaced them with TSA combination locks and sent me my stuff.
Nothing was consistent. SFO thanked me for putting my name and phone number on the case (the active duty troops all had their names on their cases as well). I don't know if I would have recovered my rifle in time to hunt otherwise. There are TSA approved locks, TSA recognized locks, and TSA accessible locks (i.e., they have a master key for them). They are all different.
Do things as best you can and be prepared for things to not be consistent between airports and even individuals at those airports.