20 mm Dummy round? 20x138B Rheinmetall “Dichtungspatrone”

Hi,
this piece came with a hole lot of others I received recently.
The Ø is 19,8 mm, case lenght is 146 mm. There is no HS except what is
visible in the picture. It looks to be a painted steel piece.
Any views on caliber and gun?Body End Tip

The answer is already on the forum, I took the liberty to make a copy/past of the answer of EOD:

EOD

Aug '12

Sorry gents, this is a German 20x138B Rheinmetall “Dichtungspatrone” of the navy for use in submarines. A chamber plug for guns installed on submarines. These were heavily greased and then inserted into the chamber of the gun and remained there as long as the weapon was not used and in particular when submerged. These “plugs” were supposed to prevent corrosion of the chamber and sowith a rough (corroded) surface of the same. Otherwise cases would not be extracted properly during firing or might even been torn apart while in the chamber. All that during an air attack on a emerged submarine whould result in a catastropy.

And a really mint exemple on this really good website:
http://212.178.67.161/avx/sites/flak2cm/generic_destination.php

Very neat item.

Ole

Besides everything having been said the caliber is 20x138B Rheinmetall for the C/30, the Flak 30, and Flak 38 AA guns.

Excellent find and in great condition. Congratulations!

Thank you all!
Interesting piece, really.