here's my thoughts on the subject. I think that you use half your rank when you are rolling for Tests (not combat roles).
The Border Ranger skill states that you to add your rank to your CS when you are using a bow during combat
. If, for example, the Border Ranger were using this discipline to, say, find his target who is hiding in the bushes after being shot at (using his knowledge of the bow to find the beginning of the enemy's arrow's trajectory), then, I believe, it would be a Test in which he would add rank/2 to his die roll.
Once he has located his target, he would then be entering combat, which would allow him to add his full rank to his CS, and combat is done normally.
As for the Dwarven Gunner discipline, I think the rule applies here as well, as it states to add his rank to CS. If the Gunner is showing off and shooting bottles out of the air, then he would be using the discipline test, not a combat roll. So he would use rank/2 to add to the roll.
I think that combat rolls and Test are two different things, which leads me to my way of thinking. Of course, I'm still going through it all, so these are my initial impressions.