Nipple threads are right hand so turning a nipple clockwise tightens it. If you are using a normal drill bit to drill out a nipple, it too is turning counterclockwise so, if your drilling from the outside of the cylinder, the drill bit will be trying to tighten the nipple.Zonie, do Colts use left hand threads on the nipples or are you trying to turn them so they go to the inside of the cylinder when they unscrew?
If you use the same right hand drill bit but you drill the nipple from the inside with the bit going thru the chamber it will try to turn the nipple in a counterclockwise (looking at the nipple from the outside at the rear of the cylinder), direction that will try to unscrew the nipple.