British aircraft machine guns of WWII

Type Weight Rate of Fire Muzzle Velocity Feed Type
Browning .303 23 lb 1140 rpm 2840 fps Belt
Browning .50 61 lb 750-800 rpm 2900 fps Belt
Browning .50 Heavy 78 lb 1100 rpm 2900 fps Belt
Lewis 26 lb 550 -1200 rpm* 2450 fps Drum usually 96 rounds
Vickers K (VGO) 26 lb 800 - 1200 rpm 2400 fps Drum usually 96 rounds

* The Lewis gun's rate of fire would "accelerate" the longer the trigger was pressed. The Lewis gun was prone to more stoppages than the Vickers K gun, and those stoppages were harder to clear. This made the Vickers K much more popular with air gunners. The Vickers K was in widespread use by the RAF early in the war and it would have been rare for a Lewis to have been used in combat by the RAF. Meanwhile the Fleet Air Arm still retained the Lewis gun early in the war, but Vickers K guns were "obtained" whenever possible.

Non- aircraft machine guns for comparison

Bren .303 23 lb 500-520 rpm 2440 fps 30 round magazine
Vickers .303 33 lb without water 450 rpm 2440 fps Belt
Vickers .50 63 lb without water 500-600 rpm 2540 fps Belt
Besa 7.92mm 48 lb 450-850 rpm   Belt