Sonny -
I'm sure this is not the only variation, but a number of 19th c. American rifles have a silver blade on a copper base (yes, copper) . I have one such, dating to 1830's, from Tennessee, and have seen several others. Don't know about Earl Long. I think a penny may have been used to make the base. As mentioned above, these sights are very shallow. Mine is less than 1/8" high, maybe 3/32."
Bill