The background for my bullet hole is the camouflage pattern of a model helicopter. For the hole's outline, I'll position the template exactly where I'd like the bullet hole to be. It's a matter of taste. Simply think about where it would fit nicely. I'll fasten the stencil with some sticky tape.
First, I'll spray a layer of black. This way the metallic silver I'm going to use will cover the background much better and quicker.
Now I'll spray the metallic silver in thin layers, until there's no more black visible. Make sure that no overspray gets onto the background.
Now I remove the stencil in order to see if I am satisfied with the result and the chosen position. Then it's on to the next step.
For the result to resemble a real bullet hole, the edges should look as if they were dented metal. I'll create this effect with a hard brush and a little bit of black paint. This I'll put on in thin lines. If a line has got too strong, I can easily repair it with a bit of metallic silver.
For the inner part, I'll then take the hole template and put it over the brushed outline. I'll spray over it lightly with a bit of black in order to fix its position.
I'll then put the outline stencil I used before exactly on top of the bullet hole again and add some light and reflections to the inner, upper and lower edges of the hole, using pro-color pearl white. Of course you may also use a plain white, but pearl white simulates the characteristic lustre of metal a little better.
Spraying with diluted black, I will create the impression of bent and dented metal.
Then I'll bring the hole stencil in place once more again, and I'll spray the hole itself using an opaque black. This is how the cavity is created.
Now I'll position the stencil for the shadow edges exactly on the outline, and I'll spray some black onto the upper inner edge. This is how the depth effect is created. Visually it appears like a thick edge towards the outside.
With a fine brush and a bit of lightened background color (or a dirty white) I'll then redefine the lower edge, thus creating a contour edge.
These few steps result in a very realistic bullet hole!