"When I'm painting I use a heat gun, much hotter than a hair dryer to the point I almost can't hold the shell as it gets it so hot. I let this cool slightly before putting on the next coat."
The missus hairdryer is pretty tip top and on the hot setting (which i use) does heat the body very hot so.....I then switch to the cool setting to cool it down
works a treat!!! Like eyeayen said some stuff is just trial and error and getting the feel for what works best for you.
Has it done this before? its just you have done a aweful lot of shells and if it hasn't done it before, is something new you've started doing to make this happen.