I freehand all of my camo. But occasionally I will use a template, the trick to getting the realistic blend between the colors is to hold the template slightly off the model. This can be done by taping short spacers (I like pennies using pennies or you can use toothpicks laid on their side) on the back of the template to keep the template from resting directly on the surface being painted. Having the template slightly above the model allows for some 'bleed over' but not much.
Each country did their own pattern, some used hard demarcation line between colors, other had a blend of overlapping overspray. Field applied camo usually was somewhat sloppy given the tools and conditions they were applied with/in.
If you freehand, you need to make sure that you always are tilting and spraying away from the demarcation between the colors to keep overspray to a minimum. Establish the colors edges then work towards the center of each color in the pattern It is challenging but with practice it can be mastered. Hope this helps.