The essay link provided by mapsjanhere refers to the earlier carbines I mentioned. Those had 17.3" barrels, flat bolt handles and a large ring action. They were never made in large quantities and were out of production by 1908. They were made originally for the old "J" bullet ammunition, but the chambers were neck reamed for the new "S" bullet c. 1905 and marked "S" on the receiver ring.
The picture linked by mapsjanhere shows the Kar 98a that was adopted in 1908 and was never chambered for any ammuniition except the S bullet. The Kar 98a has a small ring, and it looks to me like that is what the OP has. The Kar 98a does have a bolt handle cutout in the stock, very similar to that of the K.98k. Its bolt is round, but the knob is flattened and knurled on the inner side.
To compound the confusion, the Kar 98a was also called the Kar 98AZ and at one point just Kar 98. I used the terminology Kar 98a, since that is the most common term and the least confusing.