This is one of my first mods, so don't expect it to be perfect.
I wasn't really satisfied with the one that came with espedito's GTA IV weapons pack, so I looked for a better GTA IV Sniper scope and I found nothing for SA. So I decided to make it myself. I found the picture of the crosshair on GTA Wiki, made some small changes on Photoshop (e.g. unwanted particles in the picture like spots)
This is almost exactly like the Remington 700 in GTA IV.
The installation instructions is in the Readme!
UPDATE: Version 2 is out! See the difference in the screenshots. One with connected lines or dots.