For snipers, Karabiner 98k rifles selected for being exceptionally accurate during factory tests were fitted with a telescopic sight as sniper rifles. Karabiner 98k sniper rifles had an effective range up to 1000 meters (1094 yards) when used by a skilled sniper. The German Zeiss Zielvier 4x (ZF39) telescopic sight had bullet drop compensation in 50 m increments for ranges from 100 m up to 800 m or in some variations from 100 m up to 1000 m. There were ZF42, Zeiss Zielsechs 6x and other telescopic sights by various manufacturers like the Ajack 4x, Hensoldt Dialytan 4x and Kahles Heliavier 4x with similar features employed on Karabiner 98k sniper rifles. Several different mountings produced by various manufacturers were used. The Karabiner 98k was not designed for mounting telescopic sights. Attaching such sights to a Karabiner 98k required machining by a skilled armourer. A telescopic sight mounted low above the center axis of the receiver will not leave enough space between the rifle and the telescopic sight body for unimpaired operation of the bolt handle or three-position safety catch lever. This ergonomic problem was solved by mounting the telescopic sight relatively high above the receiver and sometimes modifying or replacing the safety operating lever or using an offset mounting that positions the telescopic sight axis to the left side in relation to the receiver center axis. Approximately 132,000 of these sniper rifles were produced by Germany