The Karabiner 98 kurz is a simple bolt-action rifle chambered for the 7.92×57mm Mauser cartridge that was adopted on 21 June 1935 as the standard service rifle by the German Wehrmacht.
It was one of the final developments in the long line of Mauser military rifles.
The Karabiner 98k is a controlled-feed bolt-action rifle based on the Mauser M 98 system. Its internal magazine can be loaded with five 7.92×57mm Mauser cartridges from a stripper clip or one-by-one.
The straight bolt handle found on the Gewehr 98 bolt was replaced by a turned-down bolt handle on the Karabiner 98k.
This change made it easier to rapidly operate the bolt, reduced the amount the handle projected beyond the receiver, and enabled mounting of aiming optics directly above the receiver.
The highlight of this animation shows the rifle cycling as it loads the brass five round stripper into an internal magazine.
Sources: Si vis pacem Youtube, Wikipedia