Landships II

The best information I can find about the Krupp guns of that era, is the document "Identification of the Parameters of Naval Artillery":

https://cherkasgu.net/images/our_stats/pdf/identification-of-the-parameters-of-naval-artillery.pdf

On pages 20-21 it describes the Kreiner breechblocks used by the C/64 guns.  However, I have noticed a few errors in that document (like on page 29 where it states Vavasseur invented copper driving bands in 1874, when he and Blakely actually patented them in 1866).  So some of what it says about the C/64 may also be erroneous.

The other source I can find on Prussian 1860s artillery is Volume 30 of The Engineer, from July 1870.  Specifically on pages 51-52 and 60, there is information on Prussian breech-loading artillery- though I think that is actually bronze artillery converted to breech-loading.  Still, they should be using the same Kreiner mechanism for the breech.  On page 121 there is also information on the older muzzle-loading heavy artillery of the Prussian army.

https://www.google.com/books/edition/_/rQDXqd46HugC?gbpv=1&bsq=prussian%20artillery

https://babel.hathitrust.org/cgi/pt?id=mdp.39015084712903&seq=84

(Hathitrust is slower to load but generally has better resolution in my experience)

This is one of the images on page 60.