TW,
To me, the term "heavy rolling", when talking about a balls core, is something of a misnomer, as a "heavy rolling" ball is an overall quality a ball has, and there are many factors involved in that.
Now, there are cores that lend themselves more to the process than others. The main factor, to me, is having a lower rg number. Usually, the lower the rg number, the easier it is to get it into a roll, as the mass is more centrally located in the ball, and gives the ball an earlier rolling nature than it would have otherwise.
BUT, to get the total picture, you must also factor in the balls coverstock friction qualities, the drilling used on the ball, the friction available on the lane, and the individual bowlers release.
Take, as an example, the new Forrest Green Quantum. It has a relatively high rg core, which doesn't lend itself to an early roll, yet the ball still wants to roll early, due to the aggressive cover and the dull finish. Those factors weigh in more than the core, and the ball ends up being kindof early, and oretty "rolly" by nature.
Now, as far as asymmetric cores, they can be classified either way by using the same "rule of thumb" as symmetric cores, by looking at the rg ratings.
Yes, you can fine tune the asymmetric cores by using specific placement of the psa, and make them a bit "rollier" than they would otherwise have been, but if you need to be that specific, you were probably looking at the wrong ball to begin with.
Mass bias, for me, is only a tuning tool, not a reaction building tool. If I have a poorly reacting ball, having the same ball with the mass bias in a different spot really won't help me. If it's the wrong ball, it's just wrong.
There are lots of guys here, many more learned than myself, who should chime in on this subject. I have given you what I have, but there is still much more out there.
