Oops. I'm thinking of the clips that come from Sig, Brodak, Sullivan, etc.
Those are the Luxon clips. They have been banned at various times for the tendency to open up and then straighten themselves out. They are brass underneath the plating.
Randy's "Hello Kitty" clips* work similarly, with a spring replacing the sheet metal catch, and are made of steel. There is no way they are opening up in flight, nor would they straighten out.
*a name I believe I coined, no doubt to Randy's joy.