Berezin B-20

The Berezin B-20 (Березин Б-20) was a 20 mm caliber autocannon used by Soviet aircraft in World War II.

Development
The B-20 was created by Mikhail Yevgenyevich Berezin in 1944 by converting his 12.7 mm Berezin UB machine gun to use the 20 mm rounds used by the ShVAK cannon. No other changes were made to the weapon which was pneumatically or mechanically charged and was available in both synchronized and unsynchronized versions. In 1946, an electrically-fired version was created for the turrets of the Tupolev Tu-4 bomber until the Nudelman-Rikhter NR-23 cannon became available. The B-20 was a welcome replacement for the ShVAK because it was significantly lighter - 25 kg (55 lb) to the 40 kg (80 lb) ShVAK - without sacrificing rate of fire or muzzle velocity.

Specifications

 * Ammunition: 20×99mm
 * Empty weight: 25 kg (55 lbs)
 * Muzzle velocity: 750–770 m/s (2,460-2,525 ft/s)
 * Rate of fire: 800 rounds/min (600 synchronized)
 * One-second burst-mass: Unsynchronized, 1.27 kg (2.8 lbs); Synchronized, 0.95 kg (2.1 lbs)

Production
The Soviet archives register the following production numbers by year:
 * 1944 — 2,275
 * 1945 — 7,240
 * 1946 — 440
 * 1947 — 780
 * 1948 — 1,686
 * 1949 — 2,931