If a paper target is hit with different weighted plastice airsoft BBs(.15, 20, and .30mg), and assuming that velocity is constant (appx 475 FPS airsoft gun) and distance is constant (at 25 feet) between tests, do you believe the target hole will be bigger, smaller or unchanged with the different weighted BBs? And why?

If each of the BBs is traveling at sufficinet speed to go through the tarhet and not just bounce off it, I would expect all the holes to be roughly equal to the diameter of the BB. So if the 30mg BB is larger in diameter than the 15mg BB, its hole will be larger.