I think that MG 151/15 or /20 was the closest match to 50cal in german arsenal. It was mostly used on aircraft though. Seems like ground forces didn't really have a need for heavy machine gun.
20mm mg151/20 as mounted in post war french helicopter.
MG 151/15 (1935)
caliber: 15 mm
lenght: 1960 mm
weight: 42,7 kg
cartridge: 190 g
bullet: 72 g API, HE/T, Hartkern
ROF: 700 rounds/min
MV: 1040 m/s
MG 151/20 (1937)
caliber: 20 mm
lenght: 1710 mm
weight: 42,5 kg
cartridge: 220 g
bullet: 115 g (API, HE/T), 92g (Minengeschoss)
ROF: 750 rounds/min
MV: 710-805 m/s (depending on ammunition)
I didn't find any penetration figures for MG 151/15. Seems like good light armor killer considering it's high muzzle velocity, projectile weight and availability of tungsten ammo (this was used by LW in ground attack missions).
Number of these guns produced must have been really high since nearly every LW fighter had 1-4 pieces of these as its standard armament.
IIRC they installed some "Drilling" 3x MG 151/15 and /20 mounts to SPW 251 halftracks.