Here's what I fly with. Bought it at Cabelas about 20 years ago, I don't see them in their online catalog anymore. I use this case whenever I travel with my rifle.
A TSA agent told me a couple weeks ago as I was checking my rifle in this case that some of the cheaper plastic cases he has seen can be broken into with two screwdrivers and they prefer something more solid. He didn't say metal or plastic, just not a cheap case.
This has the rod that goes through 4 loops and folds down to place an ordinary padlock. Only one lock required, I keep a spare inside that uses the same key. I used non-TSA locks and they worked fine.
On another note, I carried ammunition in a small plastic ammo box manufactured by Plano. I did use a TSA combination lock on this box, with a spare lock inside. When I checked my bag with this container inside I disclosed it had ammunition in a locked container. The only question was if the ammunition was in the original factory box. I said "yes" and they tossed the bag on the conveyer to load on the plane.
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