That varies greatly, dependent on a number of factors, such as whether it's a Gewehr 98 or a Karabiner 98, and, especially in the case of the K98, whether it's pre-war production or wartime...
The numeric value depends on the system of units used. 9.8 meters/second2 is the value if you use the SI system. If you prefer feet to meters, it is about 32 feet/second2.The amount of gravity...