It is my understanding that the blue plastic cartridge was made by Bakelittfabrikken as an experimental plastic version of the “9 mm kammarpatron m/39”, as John suggests. I can find no documentation for this, though. The text on the box label is strange, and would translate as follows:
50 cartridges, blank, plastic
for 9 mm pistol and machinepistol, 30 pieces
Month November Year 1959
Swedish type (??something about “pipe” which means barrel)
An image of the label would be fine, but it is most likely that this is an “ordinary” Box for blank cartridges used for convinience, as the cartridge is obviously not a blank. The mentioning of “Swedish type” and something that could indicate the need for changing the barrel (in brackets) makes sense as John says, as you had to change the barrel of the CG m/45 to use the kptr m/39.
The mentioning og both 50 cartridges and 30 pieces is strange. A Guess could be that both “30 pieces” and "Swedish type"etc is printed on the box With a rubber stamp or something, and applies to the New content in the Box, not the original content.
I also have the red “case” which is too long to fit in a 9mmP Chamber when you put on the end piece. Mine comes from Bakelittfabrikken, but I have no idea of what this is. Neither have the current employees at BF!