Hud on Weapon

Option 1:

Use this UnityWiki Script you can create a sprite sheet attached to an object to loop through your sprite sheet.

The script was all messed up when I went to that link I reformatted it and cleaned it up for easier reading.

You could hook into this script with a trigger to update the index, set it manually or do anything else you wanted to do

 public class AnimatedTextureExtendedUV : MonoBehaviour {
     //vars for the whole sheet 
     public int colCount = 4; 
     public int rowCount = 4;//vars for animation 
     public int rowNumber = 0; //Zero Indexed
     public int colNumber = 0; //Zero Indexed 
     public int totalCells = 4; 
     public int fps = 10;
     //Maybe this should be a private var
     private Vector2 offset;
     //Update 
     void Update () { SetSpriteAnimation(colCount,rowCount,rowNumber,colNumber,totalCells,fps); }
     
     //SetSpriteAnimation 
     void SetSpriteAnimation(int colCount ,int rowCount ,int rowNumber ,int colNumber,int totalCells,int fps ){
         // Calculate index
         int index  = (int)(Time.time * fps);
         // Repeat when exhausting all cells
         index = index % totalCells;
 
         // Size of every cell
         float sizeX = 1.0f / colCount;
         float sizeY = 1.0f / rowCount;
         Vector2 size =  new Vector2(sizeX,sizeY);
 
         // split into horizontal and vertical index
         var uIndex = index % colCount;
         var vIndex = index / colCount;
 
         // build offset
         // v coordinate is the bottom of the image in opengl so we need to invert.
         float offsetX = (uIndex+colNumber) * size.x;
         float offsetY = (1.0f - size.y) - (vIndex + rowNumber) * size.y;
         Vector2 offset = new Vector2(offsetX,offsetY);
 
         renderer.material.SetTextureOffset ("_MainTex", offset);
         renderer.material.SetTextureScale  ("_MainTex", size);
     }
 } 

Options 2: Create an empty game object. Add a mesh. Texture the mesh an appropriate background texture (in your image above it would be the blue backer). Add a 3d text object for current bullet count, and a 3d text for out of bullet count. Create a prefab and attach this script to your ammo counter object.

Extended Node: You might need this shader from the unity wiki Shader script

 public class AmmoCounterScript : MonoBehaviour {
     
     public TextMesh AmmoLeftMesh;
     public TextMesh AmmoInMagMesh; // Include any other text you want in the sam fashion
     
     public int AmmoLeft = 0;
     public int AmmoInMag = 0;
     
     public bool DidChangeAmmoCount = false;
     
     void Update () { 
     // Not sure if this is really an optimization but it doesn't hurt
         if (DidChangeAmmoCount) {
             AmmoLeftMesh.Text = "" + AmmoLeft;
             AmmoInMagMesh.Text = "" + AmmoInMag;
             DidChangeAmmoCount = false;
         }
     }
     
     public void ChangeAmmoLeft(int newValue) {
         AmmoLeft = newValue;
         DidChangeAmmoCount = true;
     }
     
     public void ChangeAmmoInMag(int newValue) {
         AmmoInMag = newValue;
         DidChangeAmmoCount = true;
     }
     
     public void DecrementAmmLeft() {
         AmmoLeft--;
         DidChangeAmmoCount = true;
     }
     
 }