Trench Art provenance ww1 shell

[buckaroobanzai]

Greetings, I recently purchased a WW1 German shell casing and was wondering if anyone can figure out which gun it came from. It is 51cm in circumference (20 inches), and has the following markings:

802
Aug 1918
KARLSRUHE
PATRONENFABRIK
Sp255

I was told by the grandson that Patronenfabrik was the company name, Karlsruhe the place of manufacture. He said Sp255 is an inspection mark meaning "spandau", and 802 refers to the quality of the metal of the shell.

Can anyone shed light on how much of this information is correct, or from which type of gun this came from?

All the best,

Bruce

p.s. If Karlsruhe was the place of manufacture why is Spandau on the inspection mark?

picture on this link:

http://atomiczebra.blogspot.com/http://atomiczebra.blogspot.com/

http://atomiczebra.blogspot.com/