Because I didn’t see the message? There are many messages, and I personally don’t spend most of my time reading these boards.
There are also plenty of tutorials, walkthroughs, and starter projects (including on the marketplace) that show how to apply decals. There are some bullet hole decal projects I can think of right now, all of which do it right, so, worst case, you could have answered this question with a $9 purchase.
(I personally like purchasing projects just to see how other people solve problems. Sometimes, their solution isn’t great. Other times, I learn something new. A dozen dollars is super cheap education, especially compared to modern college costs in the US 
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