The photo is a little out of focus. Is that proof mark; 6/5mm over 58 ?

I was looking at a Sauer & Sohn "Tell" rifle (a snap-lock, single barrel, double triggered rifle retailed by Louis Knappworst in Braunschweig). It was proofed in 1930. It was marked 6,4mm over 58,1/2 which turned out to be a 6,5x58R Sauer cartridge. That is to say, when I produced one, it dropped in without any resistence.