ID help

I aquired some plastic 9mm rounds some were 9 x 19mm parabellum but two have a 21.8mm case length. All other measurements are the same as the 9 x 18mm. The preveous owner had Denmark printed on the side of one of them. The rounds have an aluminum base with a copper primer and no headstamp. The bullet has four segment grooves across tip, looks like a break-away type bullet. It dosn"t seem logical that they would be a 9 x21 IMI rounds but what are they?
Thanks in advance

Unfortunately, your description of your blanks is incomplete. I assume that the 21mm case-length plastic blank is red in color. If so, it is Danish. It is for a submachine gun. There are brass blanks of similar case length from Denmark as well. They changed to the long “case mouth” (it is not really a case mouth in thie case of the blanks, since the “bullet” and case are one piece, but rather a headspacing shoulder) on the brass blanks sometime between 1960 and 1965. These blanks, brass or plastic, are classified as 9mm Parabellum cartridges, not as “9 x 21m/m” because of the weapons in which they are used. In Denmark, they are known as the "9mm l

The cartridge can bin sen her

Thanks John
You were correct with the red color and the explanation fits perfectly to what I have.