What recticule pattern/design did the swiss sniper K31's have?
Which K-31? There were 3 sniper variants of the K-31.
There was the K-31/42-43 - which used a Kern scope (prismatic type). IIRC, it was a single heavy post sight - like the early Mosin reticles. The 42 had a 1.8x scope, the 43 had a 2.8x scope.
The K-31/55 (Zfk-31/55) used a 3.5x scope with a post and crosshair. Might have been other variations of the reticle, but the ones I have seen have a post/crosshair.
There were also some Meiji 8x scopes fitted to the K-31/43's as expedient rigs until the Zfk-55 arrived, and they used the same post/crosshair. I have one of those scopes on a 31/43.