"I've never seen anything that supports the MG151/20 ever carrying a full belt of Minengeschoß. One in five rounds is what I understand was historical."
Well, the beltings that the pilots requested could be almost anything but the standard beltings listed in Galland's Schiessfibel from 1944 lists these: against bombers 1 Pz + 1 Brand + 1Mine, against all other targets, 1 Pz + 1 Brand + 3 Mine. The composition of tracers was up to pilots discretion. The 1+1+3 belting raises the hitting power of 151/20 roughtly to same level as that of Hisso, which we do not have in AH, AFAIK.
When the minengescoss was introduced it was mixed also with earlier and weaker HE which was obviously phased out of service by 1944. You can recognize the predecessor of MG151/20 the MGFF/M from suffix to be able to shoot also Mine rounds.
In WW2OL you can see the standard belting to consist one AP and probably 2 HE and 2 Mine when you fire five rounds and after 800-900 meters the self-destruct fuse of the HEs and Mines go off so four black puffs of smoke are visible (and if they explode near you they let out quite a bang!).
-C+