This mystery of cracked balls sure needs solving.
I've had balls crack from the outside due to impact and thin covers.
Orange Eruption, Mass Eruption
And have had balls crack from the inside
Hyroad.
I've seen cores swell, in which my IT was no longer flush
Marvel S, Hyroad Pearl, and I've seen other cores swell as well but just in Storm balls 900 Global and Motiv. In fact, what's strange is I hardly used these 2 balls, and started using them 3 years later and the cores swelled pushing the IT out farther, about 1/8" of an inch. It just happened over night like how a mushroom grows. For 3 years they were stored in the original packaging, and then stored in 3 ball totes when it happened.
I think the material used in the cores is constantly curing like concrete, and something triggers a chemical reaction in which the core expands in size, but not sure what that trigger is. The result expands the inner filler and puts an enormous amount of inner pressure or force on the cover stock. I think Hammer has the right idea, by wrapping the core in a carbon fiber shell to control the expansion. Sort of like wrapping concrete in steel. I've had several pairs of Black Fly sun glasses, in which the glass lens expanded faster than the metal frame causing the frame to split. That's why almost all sun glasses now use a polymer lens, so they have the same expansion rate.
The plastic bag the balls come in seems to be the best protection.
Why do you think the core swells? Did you do anything to test that?
I've had a couple crack and it was the cover that shrank, not the core swelling. We placed the steel ring(not sure what it's called) used for measuring size at the pro shop, the ball just slipped right through. That is proof the ball diameter was reduced in size. The IT stuck out to far, the IT hole became smaller and the pin plug was raised, but it wasn't the core swelling, it was the cover shrinking. I've had a couple of Storm balls in the past do this, and some of the older Lane Masters/Legends stuff did it as well.
Proof would be if you knew for sure that the ball was larger when new. They do have balls of all sizes after manufacturing and I am not sure which ball ring size they use in the factory. I remember when the Brunswick 8583 came out that they sent a ball ring to the local pro shop and he used it to verify the 8583 balls were larger than the ring. The marketing for the 8583 was that they were larger. Some other balls, even from Brunswick, the ring would slip right on over.
Of course, that was close to fifty years ago so I am not sure what size the balls are being sent out as now, but to get back to your proof statement and I am not saying that you are incorrect, but unless you knew for sure what size the ball was before it aged or cracked, you can't be sure that it was smaller now. If the ring did not slip over the ball when it was fresh out of the factory and it does now, that would be proof of shrinking.
Personally, I too think that the coverstock could be shrinking and that the harder denser core material is shrinking at a slower rate, thus causing pressure on the coverstock, but I don't own one of those rings to do any type of testing.