intended to increase range. These included experiments carried out in 1940, with 162 mm barrel firing 162/100 mm shells. The barrel was damaged during the experiments; additionally, the gun was found to have unsatisfactory ballistics and problems with loading. Firing 152/107 mm shells failed to produce significant improvement in range. Br-19 The Br-19 was an experimental piece which combined elements of late production Br-2 (breechblock, barrel with deep rifling) with elements of B-30. The gun was tried out in 1939; it found superior to the Br-2 and was recommended for production, which, however, never started. Br-21 The Br-21 was an experimental 180 mm gun developed privately at the Barrikady Plant by mating Br-2 barrel bored out to the 180 mm caliber to carriage of B-4. The gun reached trials on 20 December 1939. The gun turned out to be more powerful and accurate than the Br-2, but was never adopted, because of the need to produce a new ammunition. Production The Br-2 was in production from 1936 or 1937 to 1940. At least 37 pieces were manufactured. Early pieces had barrels with the original "shallow" rifling (at least seven, built in 1936–37), while late production pieces had barrels with the newer "deep" rifling (27 in 1939–40). Description The Br-2 had a long - 47.2 calibers - barrel of free-tube construction, with interrupted screw breech. The recoil system with variable recoil length consisted of hydraulic recoil buffer and hydro-pneumatic recuperator. The gun utilized bag loading ammunition. For assistance in loading, a special hoisting crane was used. The single trail tracked carriage was essentially the same as used for the 203 mm howitzer M1931 (B-4) and the 280 mm mortar M1939 (Br-5). It included an equilibrating mechanism of pushing type. The carriage allowed transportation of the weapon to short distances with the speed of 5–8 km/h. For longer distances, the barrel was removed from the carriage and transported separately on a special cart. In this case, it took from 45 minutes to two hours to prepare the weapon for combat. Several types of carts were used for barrel transportation. Guns produced in 1937 received the Br-6 cart. Other types used were the wheeled Br-10 (11.1 tons with the barrel) and the tracked Br-29 (13.42 tons with the barrel). In the trials report of 7 August 1938 both were referred to as unsatisfactory; the former because of bad passability and the latter because