Suppose you have two balls a Track and an Ebonite.  Both balls look to have a similar weight block and have surfaces of 500/2000 Abralon.  The Track ball has an RG of 2.48 and a Diff. or .041.  The Ebonite has an RG of 2.49 and a Diff. of .048.

Based on this information (both balls being drilled alike and used on the same oil pattern) I would expect their length to be very close and the Ebonite ball to flare a little more with a possible increase in overall hook. 

Would this be a good assumption?

Cover has a very big impact.  Even things like pigment seem to make a difference in reaction . Also different cores, even with the same or very similar specs can match up differently. 

I agree with Charlest's explanation with one small exception........."So your assumption is false and dangerous".
False I understand, but why is it dangerous, will the ball explode?, fall off his hand and crush his foot (or someone else's)?  Just can't get my head around the dangerous part of the comment.  But maybe Charlest knows something I don't and should, so I'm not in harms way. lol 

I agree with Charlest's explanation with one small exception........."So your assumption is false and dangerous".
False I understand, but why is it dangerous, will the ball explode?, fall off his hand and crush his foot (or someone else's)?  Just can't get my head around the dangerous part of the comment.  But maybe Charlest knows something I don't and should, so I'm not in harms way. lol 

C'mon already! 
Never heard of a dangerous assumption??
Those could be the cores of 2 wildly different balls. One could be for medium-heavy oil and the other could be for light oil - was all I meant.

Dangerous because someone could believe bad information, and trust me, trying to weed out the bad information is very difficult. Can't tell you the number of times someone has walked into the pro shop and said we were wrong because of what he/she read on the internet or from what someone else told them. We then have to spend time (which is ok) to show why the person is wrong and educate them with the correct information.

As for the OP question...I will take an extreme example. Take 2 Black Widows, same core, same company, and drill them identical. In your theory, because they have the same core and we drill the two balls identical, the ball will react the same/close to each other. However, after revealing that one is the Black Widow Spare with a plastic cover and the other has a traditional cover, the only difference is cover and I bet you will see tons of reaction difference.

So yes, covers drive ball reaction and the core allows you to fine tune that reaction.

Dangerous because someone could believe bad information, and trust me, trying to weed out the bad information is very difficult. Can't tell you the number of times someone has walked into the pro shop and said we were wrong because of what he/she read on the internet or from what someone else told them. We then have to spend time (which is ok) to show why the person is wrong and educate them with the correct information.

As for the OP question...I will take an extreme example. Take 2 Black Widows, same core, same company, and drill them identical. In your theory, because they have the same core and we drill the two balls identical, the ball will react the same/close to each other. However, after revealing that one is the Black Widow Spare with a plastic cover and the other has a traditional cover, the only difference is cover and I bet you will see tons of reaction difference.

So yes, covers drive ball reaction and the core allows you to fine tune that reaction.

To further the Black Widow example, the RG and Diff numbers for the Black Widow Spare are different than the "reactive" Widows (especially in the 12 and 13 pound versions) despite the balls having the same core.  When I asked Hammer about this, they replied that the density differences of the cover material between the resin and polyester balls is substantial enough to cause RG and Diff changes even though the cores are the same.  So, cover material and prep matters.