Actually the Berezin B-20 (3-gun La-7) was the lightest 20 mm aircraft cannon of the war, and by a large margin. It was essentially a up-chambered UBS 12.7 mm. It weighed less than a .50 cal and half that of the Hispano II, while firing the same 20 mm round as the ShVAK. The ShVAK wasn't anything special, weighing the same as an MG 151/20.