The MSR is described in the game as:

This bolt-action fires with surgical precision

You’ll find it in western Montuyoc province, inside the mine. The story mission “Carl Bookhart” is nearby. The weapons case is at the end of a mine shaft, all on its lonesome.

You can only access the mine itself via the main entrance at the mining camp, where there are four bad guys plus one sniper. Take out the sniper and sync shot the rest to get into the mine. It is dark in the mine, so you may need night vision or infrared to see. After you enter and take out the first couple of bad hombres (one on a mounted gun), take the first shaft off the the left, and go straight, all the way to the end – taking out anybody in your way, and there it is!

Oh boy. This is everyone’s favourite sniper rifle, right? Mmmmm… not mine. I wanted to love the MSR! I mean, it looks damn cool, and sure it’s powerful and precise, but heaven forbid you miss a long range shot.

This gun takes what feels like ages to rechamber another round, so your target will almost certainly have run for cover before you get another shot off. Unfortunately, it’s also slow as hell to reload.

On the positive side, this is a reasonably customisable sniper rifle (MSR stands for Modular Sniper Rifle, after all). The standard magazine is a tragic 5 rounds, but there’s a 10 round extended mag available in Remanzo which is useful for when you are hitting targets, and don’t want to be reloading when you’re in the zone.

You’ll need a good scope for this gun, and there are plenty available, but the TX5i Tactical has the highest zoom, found in Koani and is highly recommended. Also worthwhile is the long barrel accessory for added damage and penetration which you can pick up in San Mateo.