Never seen this picture before, presumably they would use whatever weapon is at hand? german soldier | Flickr - Photo Sharing!
see post #6 here. http://www.ww2talk.com/forum/weapons-technology-equipment/37259-bren-gun-photos.html
And here mate: http://www.ww2talk.com/forum/general/6921-captured-ammo-3.html#post192092 For what it's worth, I think that particular FJ has a good face, despite his naughty appropriation of His Maj's equipment...