Motiv and Lane 1 puts the same size and shape core in all of their ball weights.
You do realize that in the lighter versions of most of Motiv's balls, the core specs/numbers are usually no better than the generic cores of other companies? It sounds like you think you're finding the same exact core in a 12 pound Primal Rage as you're finding in a 15 pound Primal Rage. Please correct me if I'm wrong...
You are wrong, as the core specs/nos are better in Motiv balls than most balls in other companies. When I first had serious health problems in 2012 and then back surgery and being told to drop to 12# in 2013, I checked this out with Motiv, Brunswick, Storm, Ebonite, and Lane 1 and found that Motiv and Lane 1 were the only companies that put the same size and shape but less dense core in all of their balls regardless of ball weight, to give the lighter balls the same shape and movements as close as possible to the heavier balls.
The core in a 12# Rage is the exact same size and shape as it is in a 15# Rage. Go to the Motiv site and check the specs on all of their balls and you will find that the specs on 15# vs 12-13 lbs are very close with little difference between them. If a specific ball in 15# has an "xx" rg and "x" differential, you will find the 12# & 13# balls rg and differential are almost the same. If a specific 15# ball has an "xx" rg but a lower differential, you will find the 12# & 13# balls are almost the same.
Go to the Brunswick site and you will see for example, balls in 15# having say.050 differentials and their 12# & 13# balls will have differentials in the .020 something range. You won't find those type differences in Motiv. (note... I was a Brunswick guy at the time of all of my health problems, but per the example just given, I had to switch to Motiv because of that. Other wise, I would still be throwing Brunswick)
FYI, I have a 13# Primal Rage and it's rg and differential ( 2.60 & .055 ) are almost the same as a 15# Primal Rage ( 2.55 & .050 )
I have a 13# Octane and it's rg and differential ( 2.58 & .047 ) are almost the same as a 15# Octane ( 2.55 & .043 )
I have a 13# Tag and it's rg and differential ( 2.59 & .038 ) are almost the same as a 15# Tag ( 2.55 & .037 )
You won't find nos that run that close between ball weights in most other companies balls. It appears that Storm does something similar to Motiv in certain but not all balls whereas Brunswick only does it in one ball the Strike King and Ebonite likewise with the Cyclone