You don't necessarily need a lower RG ball; besides going from 2.5 to 2.46/7 isn't much of a jump.
What you need is the right ball; you cannot separate a ball into its component parts: coverstock and core. There's an old saying: the whole is greater than th esum of its parts. That is never more true than when it comes to bowling balls. People keep on saying I loved this ball's reaction and it has this XXX core; then in his mind he tells himself,"therefore all balls with this core will all always work great for me under all circumstances." Ain't gonna happen, dude!
You might just need to take the FM down to 600 grit or you might need to drill one up with a lower pin position Plus the MB closer to the VAL, with a weight hole in the thumb positive quadrant.
You might need any number of things, but there's no guarantee that a FM with a .003" lower RG will help you. By the way, that is 3 thousandths of an inch!
ADN you might get that change or more by just moving the pin from 4" to 2.5" from your PAP.
oh, and the AMB particle is sigificantly more aggressive in oil than the FM, no matter what the RG is.
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"...for advice is a dangerous gift, even from the wise to the wise...."
J. R. R. Tolkien