I have wanted to try this as well...same with sand blasting... the color and finish is certainly next level compared to the rattle can! No doubt you'll figure it out as you always have awesome end items!! Look forward to.more of it!!
It probably didn't get covered because it had contamination in that spot. You should out gas before you powder coat any part that has come in contact with grease or oil. On the hinged part, the top and bottom were too close together. Possible Faraday effect. The powder was being repelled. Open the hinge more and connect to a better ground. The ground on that gun isn't the best.
