The weapon was effective to about 300 yards (280 m) as an anti-tank and anti-vehicle weapon. There were two main service loads used during the Second World War, the W Mark 1 (60 g AP at 747 m/s) and the W Mark 2 ammunition (47.6 g AP projectile at 884 m/s). Later in the conflict, but too late for service use, a much more effective high velocity round was developed, this fired a tungsten cored Armour-Piercing, Composite Rigid (APCR) design at 945 m/s. The W Mark 2 projectile was able to penetrate up to 3/4 inch (20 mm) of armour at 100 yards (~91 m). The armour plate inclined at 70° from the horizontal ie 20 degrees from the direct line angle of fire - the effective thickness being ~21.5 mm. Its effective range against unarmoured targets (e.g. infantry), was much further.
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