This was another Folded Case experimental by the US during the mid 70’s
The following from Buttweiler (RTB.VII.2.306)
Produced as a promotional item, this is the 4 piece bicentennial set. It was produced to commemorate the American Bicentennial and the set includes 4 colours representing the 4 various loadings generally seen in small arms ammunition. White/Cream = BALL loading, yellow = TRACER, blue = INERT, green = PROOF. Each has a raised FA 1976 headstamp, but they were not produced by Frankford Arsenal.
Base shown at 200% scale