Airfix C-47; Painting it (or attempting to)

Obviously it's going to be one of THOSE models. I sprayed the undersides without any issues, masked the model then applied the top colour. I was'nt happy with the mix of paint (Tamiya XF-62 Olive Drab and XF-52 Flat Earth) plus the paint had gone grainy on the wing roots. I gave the model a quick rub down when dry and mixed up some XF-58 Olive Green and XF-52 with some X-22 Clear thrown in and I ended up with this;

Yep the paint is still grainy and it also highlighted the areas that had been rubbed down (badly by me) so it's going to be left alone while I think about it. Oddly enough after cleaning the airbrush of green paint I decided to matt varnish the Trumpeter E-25 with Mr Color and I had all sorts of issues in the past with frosting and grainy finishes however this time it sprayed perfectly. Weird!