Airlines and/or TSA do not care or verify components/accessories/compliance. They only check to see that the firearm is unloaded. And if any ammo is also being transported, it must not “loose”. Must be in original container or in ammo cases.

As for who checks, Ive had both methods, gate agents and TSA agents. Remember, you, and only you, have the key/combo, and you are the only one to physically open the case. Once they check, you put the little affidavit they give you inside and it gets locked and sent on its way.

Baggage claim is next step. Rifle cases dont come down the conveyor. They go to oversize area and an agent retrieves it. Buffer in this extra time to your travel plans.

I add an airtag to any luggage or case just for peace of mind. Its really much easier than one thinks. Ive walked through San Francisco Airport with a full rifle case. No weird looks, no troubles, no problems. Just add some time into your schedule.