Still choosing a reference sniper, must be compact and lightweight.
After all, the – almost non-existent – back-story of the game does not include an organization behind our sniper, so rifles wouldn’t be dropped in the chosen place by someone else, he would have to carry his own, from home or whatever place he came from. Also, considering the game play – you choose your own place to shoot from – it wouldn’t even make sense to have a rifle dropped at 10 (or more) different places.
So we can be pretty sure he wouldn’t be carrying something like a CheyTac Intervention – this being, from memory the longest sniper I read about – sure it’s a nice rifle with good accuracy and a long range, but almost 1.4 meters of length and a weight over 14 kilograms it’s far from portable.
So I made a small (very small) list of suitable rifles:
Desert Tactical Arms ‘Stealth Recon Scout‘ — 7.62 NATO, Weight: 5 kg, 800mm long
TEI ‘M89SR‘ — 7.62 NATO, Weight: little over 5 kg, 850mm long
RPA ‘Rangemaster 7.62 STBY’ — 7.62 NATO, Weight: ≈7 kg including scope and bipod, 710mm long when folded
PGM ‘Ultima Ratio Commando II‘ — 7.62 NATO, Weight: ≈6 kg, ≈750mm long when folded
At least on paper – sorry, no real life experiences with rifles – these should be relatively easy to transport by hand in the middle of a city without being arrested on the first 10 seconds. All of them have an effective range of 800 m or more, except the RPA rifle. So all of them are good reference rifles to use on the game.