This is just an idea I had after watching a playthrough of InFAMOUS, but why not make a map, not necessarily Blood Gulch, where all Marine weapons use sniper rifle bullets of varying power?

The AR can use bullets at a fifth of the power, pistol at a third, shotgun at a fifth, and so on.

I'd do it myself, but I haven't downloaded 3DS MAX yet, and I don't know enough about creating or modifying maps, aside from the little bit of experience I have from Unity and Game Maker.