here i have a compárison of bullets from Fighters of Battle of Britain
A comparison photo of the ammunition used in the Battle with some other rounds is HERE:
from left to right
1) the .303 British (7.7x56R) (Spitfire and Hurricane)
2) .5 inch Vickers (12.7x81)
3).50 Browning (12.7x99) (P-47) (P-40)
4) 20mm Hispano (20x110) (Spitfire 1941)
5) 7.92mm v-Munition (7.92x57) (Bf 109E and Bf 110C)
6) 20mm MG-FFM (20x80RB) (Bf 109E and Bf 110C)
7) 15mm MG 151 (15x96) (Bf109G)
20mm MG 151/20 (20x82) (He 162),
9) 13mm MG 131 (13x64B)