Storm Bowling has come up with a great marketing tool. They Call it the PRO PIN, or PRO CG Ball. I say marketing, because that is what it really is.
These balls are nothing more than what the other companies call blems or 2nds. The marketing staff has come up with a way to sell these and not call them what they really are.
A Pro pin happens when the pin is longer than a certain set length such as 5 inches. The length of the pin is usually used to tell you what the length of the break point will be. These balls have exceeded that length and are only good for very high rev players and will give them length and snap. (Most bowlers do not fit in that Catagory) These balls can be drilled but the driller is very limited in what they can do for the customer in this case.
A "Pro" CG happens on a ball when the Center of gravity falls out of line with the pin and the Mass Bias. In a First quality ball you look for these 3 things to be exactly in line, or very close to it. When it is out of line you have to use larger weight holes to bring the ball back to USBC Legal specs. It can also keep the ball from being drilled in the proper manner for the results that you want to see. In many cases it will cause the mass bias to end up on the wrong side of the thumb hole. For a right hander the MB should be to the right of the Thumb, And a Left Hander, to the left. If these are reversed the reaction of the ball is greatly diminished.
...read the full guide with pics here