As light tank development progressed through the interwar years, most nations worked on producing antitank weapons for the infantry. Early on, this was done by solid projectile, as early tanks were relatively lightly armored. Armor was quickly increased during WWII, and solid bullets had to be replaced by explosives for effective infantry antitank weapons. However, at the outset of the war many countries had large caliber antitank rifles, such as the PTRS/PTRD, Mauser 1918, Lahti, Solothurn, PzB38, and Boys.
The Boys AT Rifle was put into production in England in 1937, and was effective against light tanks at that time. It was a fairly orthodox bolt action design, using a 5-round magazine and a .55 caliber (14mm) projectile at 2640fps. Initial doctrine had the Boys considered effective to 500 yards, but this dropped as the war progressed, and even with improved projectiles (tungsten core) effective range dropped to 300 yards, with 100 being recommended. While tanks became too heavily armored to be much threatened by the Boys, it continued to be useful against gun emplacements and light armored vehicles such as halftracks and scout cars.
By far the biggest complaint against the Boys is its heavy recoil. Despite a muzzle brake, recoil-absorbing stock slide mechanism and heavy recoil pad, it had a reputation for punishing recoil. As a result, it was often fired from fixed mounts, such as off a Bren or Universal carrier.
It the US, the Boys is considered a Destructive Device because its barrel exceeds .50 caliber. Between this and the scarcity of .55 ammunition, many guns have been converted to .50 Browning. This allows much more available ammunition to be used, and removes the requirement to register the gun.
We have only one piece of Boys documentation at the moment, a South African Small Arms Training manual from 1942. We are working on getting more, but in the meantime you can find a lot of good info on the Boys at rifleman.org.uk.
Stop That Tank! A Boys Rifle training film made in part by Walt Disney in 1942 for the Canadian military: