1917 Spandau

I just acquired a 1917 Spandau #359, with a crown on the receiver and the barrel stamped with an "S" just ahead of the receiver. Could someone tell me what the S might stand for?

Thanks for your time.

Spitzbohr or spitzer. In 1903 they changed rifles to pointed bullets and also altered chambering dimensions.

All the S means is it is ok to fire S ammo in it . All Gew-98 rifle from 1899 to 1918 were made with the same chambers and bore size . The S ammo was in limited use before the Gew-98 was. The Germans had two different types of ammo in service at the same time and did not make the S round standard until 1907 .