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About that detecting the surface, about that my.skin part, are you talking about the skin from the bullethole?
yeah, I forgot you aren't using a model but a sprite. So replace that my.skin with an ent_create function or something, i.e. I hope you get the basic method I explained

. I don't have your "bullet creator" function so I don't know precisely what you did.
However, before I can start with surface detection, I have to make it possible to fire at entities.
Can you verify that you do hit the models (so they lose health when you hit them), but only the bullethole does not show up? If this is not the case, then the problem could be in your shooting code rather than in your display_hithole code.
If you can hit the model but only the bullethole wont appear, then try to make the bullethole clearly visible in one place, so you are sure that it is created or not. The problem could be related to the 'normal' variable, but I'm not sure.