From the DCS K4 manual:
(The contents of this manual are based largely on actual vintage Bf 109 K-4 manuals of the aircraft’s
service era.)
Armament
The armament of the K-4 consists of a 30 mm (1.18 in) MK 108 engine-mounted cannon
(Motorkanone) with 65 rounds, and two 13 mm (.51 in) MG 131s in the nose with 300 rounds per
gun. Some production K-4s were fitted with the MG 151/20 as the Motorkanone. Additional
Rüstsätze, or equipment kits, such as a 300 L (80 US gal) drop tank (R III), bombs up to the size of
500 kg/1,100 lb (R I), underwing 20 mm Mauser MG 151/20 cannon gondola pods (R IV) or 21 cm (8
in) Wfr.Gr. 21 rockets, were also provided for.