60x64R German L/21 Boat Gun case

I got a 60x64R case at a flea market today, can anyone post a photo of a round with its projectile in place, or a diagram of a loaded round? The case mouth actually measures about 63mm, but the case is correct length and does not appear to have been cut down. The extra few mm makes me think that this could be a round that had its driving band inside the case mouth. Is that true?

I am sure of the German Navy connection with this case as it had the crown over capital M. The full headstamp is: “M PATRONENFABRIK #KARLSRUHE# V 1917 143. (”#" Indicates flaming bomb markings). Any photos/drawings/information would be helpful. How common is this case? I have never seen one before.

As far as I know it was loaded seperately. The drawing of the combat load shows a cap -

Thanks, now I know that is definitely what I have, and it is not something else cut down to similar dimensions. Were these loaded to different strengths depending on the range required? The primer shown in the drawing looks like a Second world war era primer, were these used by The Kreigsmarine during WW2? Do you have any pictures of the gun or projectiles?

Somone on another forum asked me to post a picture, so now I’ve taken it I thought i may as well post it here. For anyone whos never seen one before, here are a couple of photos:

Case (AA battery for scale):

Headstamp (sorry about the poor quality photo):

The drawing is from Reichsmarine ( until 1933 ) - the Kriegsmarine didnt use the 6cm L/21 gun - only for salut with blank cartridge (Man

Thanks for the photo and drawings. Are these cases easy to find in Germany? I paid