I doubt it was ever used in WWI as a sniper rifle. It looks like a pre-WWI purpose built sporting rifle, possibly with an Oberndorf action as justcurious suggested.

I like this rifle. I have a liking for those late 1800/early 1900 German and Austrian sporting rifles with diminutive side panel, pancake cheek piece stocks and graceful lines.

The barrel I doubt ever graced a military Mauser as it has no steps in the diameter. Whether the rib is integral to the manufacturer of the barrel, and I suspect it is, or soldered on it has a nice profile.

The profmark on the left receiver ring indicates proofing between 1891 and 1912, inclusive.

Vlad