....I am so happy! Finally found how Solothurns were transported:

[img=http://i21.photobucket.com/albums/b271/dposcuro/Other/34672_zpsfe5ae8a6.jpg]
[img=http://i21.photobucket.com/albums/b271/dposcuro/Other/20mmSolothurnCase_zps1963951d.jpg]

Couldn't find one for the S18-100 specifically unfortunately, but the S18-1000 is very closely related. Course...how the Swiss transported 20mm ammunition, I am still not sure. So I went wooden crate as best guess.