Not sure how to even approach this, Im good with unity but this and stumped me, Basicly in halo the assault rifle has the ammo counter on the actual gun and when the player shoots the ammo goes down, if you dont get what i mean im sorry but its the best way i can put it… Any suggestions are helpfull thanks 
When making reference to other game behavior, it is helpful to refer to an image or a video. So I assume you are talking about the indicator as seen in this video:
http://www.youtube.com/watch?v=aR6fsOqODaw
The indicator is “just” a child game object. You can emulate it easily using an array of textures or using 3D Text. You need a shader that supports transparency. Add on-interface packages like NGUI and EZGUI make it easy to create a texture atlas to reduce draw calls if you go the multiple-texture route.