[jlgreco]

For health it might not be best, but I think for ammo it would work well. I mean, in the real world you don't even get a HUD for ammo, unless you're in an airplane or tank I suppose. A HUD for health is necessary just because the game isn't real life, but the ammo HUD is just a convenience; you can be more creative with it.

Maybe gun models that give a visual indication of remaining ammo will become more popular.

Perhaps adding blur/color saturation filters to your entire field of view might take off as a primary indication of remaining health.