This tutorial is 4 steps and has a difficulty of Easy. This tutorial will show you to make a very good metal texture, and then add scratches or bulletholes to it.

     1. First create a new document, I'm going to use a 300 x 300 pixel image ok. All colors in this tutorial are in hexadecimal (hex) value.

     2. Now, chose a good grey color, I used 5E5E5E. Now fill your whole document with that color by going to Edit > Fill then depending on whether the color is a background, or foreground color, just select whichever it is then press ok.

     3. Now you need to go to Filter > Artistic > Sponge. Use 0 for the Brush Size, 0 for Definition, and 1 for the Smoothness. Press ok. You should now have a nice metal texture that looks similar to the one below.
Step 3

     4. Add some scratches and bullet holes if you want with the burn and dodge tools.
Step 4

     Here is a zoomed in look at the bullet hole. Here is basically what I did, I used an 8 pixel sized circle spot of the burn tool at about 80% exposure, then used the dodge tool around it at a size of 1 pixel, and 60% exposure. I made the lightest color of the metal right around the impact site by using the dodge tool more in that area.
Bullet Hole