Originally Posted by
Kent Based
The 13mm was reportedly adopted as a counter to the large US bombers. They replaced the 7.92mm in the Bf109 from spring 1943, and those in the Fw190 models in November 1943. Until those new models were available in numbers, then the older 7.92mm were still around. The 338th was first in action in May 1943, so plenty of 7.92mm around for some time still, to have hit those googles.
There's also the rear mounted gun on the Me110 among others.