SS-Oberscharführer Hans Hirning won the Knight's Cross on October 23, 1942, as a SS-Rottenführer in the 6./SS-Totenkopf-Infanterie-Rgt. 1 of the SS-Totenkopf-Division. Hans Hirning was killed in action on April 30, 1945 near Dürnholz, Czeckoslovakia.
As far as I know, Hirning was not a member of an assault gun crew. He won his Knight's Cross for destroying a russian anti-tank gun with a demolition charge as the russians threatened the german lines. So a local russian breakthrough was prevented.
Source: "Their Honor was Loyalty - An Illustrated and Documentary History of the Knight's Cross holders of the Waffen-SS and the Police" by Jost W. Schneider (1993).
According to the book by Schneider, and also supported by Karl Ullrich's "Wie ein Fels im Meer - Kriegsgeschichte der 3. SS-Panzer-Division "Totenkopf"", Hans Hirning did not recieve the German Cross in Gold.
"Wie es eigentlich gewesen ist"
Leopold von Ranke (1795-1886)