Hits like a truck, but enemies hit like a truck as well.
Firearms hits 10k, which makes the Hunter's Faith bonus perk give you 30% bonus damage per headshot. This, combined with the "One is None" perk, that there is a very real change you have a full magazine of double damage bullets. This is why I used a M700 instead of a M44, so I can up my magazine size to 15. That's 15 bullets of heavy hurt. The other mods are designed to increase the headshot damage. Prepared just further increases the damage if you're far enough away.
Elevated gives you a bonus if you're elevated, so you should always try to find an elevated position, which is pretty easy. The elevated position also gives you reasonable protection against enemy fire, so there's that. Just watch out for grenades!
The downside to this build is that you're vulnerable as can be. The low Stamina stat means that you die pretty easy. This is why some of the perks on the armor pieces are configured to give you at least some degree of protection/healing. The Healing box with Ammo modification allows you to just camp behind something, and keep firing without worrying about running out of ammo.
The purple mods speak for themselves: you can also switch them out for yellow mods, to get your Firearms even higher, but the 20% bonus damage to elites easily outweighs the low percentage of bonus damage the 600 extra Firearms gives you.
The M4 Lightweight is just there for enemies that get too close for the sniper rifle to effective (read: panic mode). The Accurate perk allows you to stay on target easier.
For the off-hand weapon, there is no real reason the M45A1 is used.You can use pretty much every other weapon as well.
The way I use this build is like follows:
This build becomes more powerful if in a team, with team members that can distract enemies for you, and take their fire. This gives you more time to pick off enemies, instead of hiding from bullets.