ROMMEL34 said:
First of all the MG 131 was a 13mm (.51 cal) heavy machine gun NOT a cannon. The MG 151 was a 20mm cannon.
While your red text, underlining and bold-italic fonts are the height of a persuasive argument, the establishment of the line between machine-gun and cannon at 20mm is somewhat arbitrary, and was not followed by all nations (although it is retroactively applied today).
For example, there is no logical reason why the MG 151/15 should be a machine-gun, while its derivative MG 151/20 is a cannon. They are essentially the same weapon firing similar explosive shells. MG 131 also fired explosive shells, and under some systems of designation would be considered a cannon. I think the designation of these weapons should make it clear that at the time the Germans were not drawing such distinct lines between the weapons. But traditionally, 20mm has been considered the smallest practical caliber to use high explosive shells in, and thus the minimum "cannon" caliber.
Really, the terms used are totally irrelevant and my main point was that the MG 131 was designed as an aircraft armament not a ground weapon, and its use in that role would have to be considered extraordinarily exceptional. I just broadly group this class of weapons under "machine cannon," as they were clearly a different family of weapons from the rifle-caliber aircraft guns derived from ground weapons.
If you want something practical in the game, how about a KwK 30 or 38 on a ground mount. Those were turned away from the sky and towards Russian lines quite regularly. Still, this comes with all the difficultly for implementation that any crew-served and not man-portable weapon is going to face.
