barrels with deeper rifling were manufactured. The B-30 barrels were also used for ultimately unsuccessful experiments with pre-rifled shells and with "Ansaldo system" variable depth rifling. While generally similar to the competing design, the Br-2 had different barrel construction (built-up vs loose liner), slightly different breechblock and featured an equilibrating mechanism. Despite results of trials, which favored the B-30, the Artillery Directorate decided to adopt the Br-2. The reasons for the decision are not clear. However, it was decided to switch to free tube barrel construction in production pieces, making the gun somewhat more similar to the B-30. Improved variants Although the Br-2 was adopted, it was evident that the gun had significant drawbacks. One of the problems was very short life of the barrel: it took about 100 shots for the muzzle velocity to drop 4%. In an attempt to tackle the problem, an experimental piece with longer (55 calibers) barrel was produced; another experimental barrel had smaller chamber and deeper rifling. The latter solution was eventually preferred and from 1938 a variant with deep rifling replaced the original barrel in production. It was claimed that the new variant had five times longer service life. However, service life of the new barrel was measured using different criterion (10% drop in muzzle velocity), so actual improvement was probably much smaller. Another drawback of the gun was its low mobility, aggravated by separate transportation of the barrel. Attempts to improve the tracked carriage (such as the experimental T-117, which was tried out in 1939) were ultimately unsuccessful. In 1938 the Artillery Directorate issued specifications for a wheeled carriage for the Br-2 and the 203 mm howitzer M1931 (B-4). The project was handled by the design bureau of Plant no. 172 (located in Perm), headed by F. F. Petrov. Because the design bureau was busy with other tasks, the development of the new carriage - factory index M-50 - advanced slowly; it never advanced past the design phase and was canceled after the outbreak of the German-Soviet War. An improved wheeled cart Br-15 for barrel transportation was considered in 1940 but was never adopted, because it couldn't improve the mobility of the carriage. It took until 1955 to develop a variant of the Br-2 - designated Br-2M - which had wheeled carriage and didn't require separate transportation. The Br-2 was also used in a number of unsuccessful experiments with discarding sabot shells,