Flakvierlings... Drillings... Why was no fusion made, ever?

The Flakvierling extended the flak 38s life in the Wehrmacht but... once the MG151/20 appeared, was no attempt made to fuse them by adapting the Mauser gun to fire the 20x128mm cartridge used by the light flak?

Did the larger cartridge pose too many challenges or did politics play a part? The Drilling would eventually appear out of desperation, since it used a weaker round, but it is hard to believe this "fusion" wasnt considered at some point.

Otherwise it would appear to be a very convenient arrangement that would simplify logistics, increase lethality and lower personnel requirements...

The light flak used a case that 138mm long and rather fatter than the 20 X 82 mm case the MG/151 used. The 20 x 138 was much more powerful than the 20 x 82 and by the time they got done it would have been a brand new gun sharing little more than the design concept of the MG151.

a bit crude but gives the idea.

Thx, I expected as much given the size difference between the rounds, but I havent found anything about it even being considered nor proposed... or the other way around, just adopting the MG151 in either 15mm or 20mm as light flak, I expect the fist one to be a better option thanks to its higher speed.

The MG 151 as an AA gun faced a few problems. Not that it couldn't be used but it wasn't ideal.
The 15mm while better than the American .50 cal from an effectiveness point of view, was heavy, expensive and used a small shell with only a few grams of explosive, it still used a fuse though (expensive) .

Anthony Williams photo.
Not sure on barrel life, (the US .50 was rather short lived until 1944) but the high velocity gives good effective range, most AA ranges in books are total nonsense.
The 20mm solves several problems and introduces a few of it's own. Barrel live will be better, it carries more HE (forget the mine shell for AA work) for more target effect, fuse is bigger but not much more expensive ( about the same number of parts and time to assemble) but the lower velocity means a shorter effective range than anybody else's 20mm AA gun. The 2110 in the picture is for a Hispano but it used the same projectiles and had the same velocity/range as the Oerlikon.
The rate of fire of the MG 151 is good.
The mine shell starts out fast but slows down very quickly, by 300-400 meters it is moving slower than the regular 20mm MG 151 ammo and this makes aiming a problem. There were no mine shells with tracer so once past 300-400 meters the tracers rounds are not showing you where the mine shells are going.

Given the low HE content and poorer ballistics of the available HE rounds, I think a 15mm API-T projectile would have been the better choice for AA work, even on a twin mount they could have offered lower weight and a higher RoF than the flakvierling (specially since usually only two guns fired at a time), less crew too, the large number of tracers would have been a nice deterrent although its shells would have been less effective. Thicker barrels would have been needed to manage the heat though...

Even a quad Mauser with non-mine ammunition sounds more attractive.