If I am reading this correctly--the MB will be in the same spot for both drillings correct? So, the difference would be the pin placement <3 vs. 4.5>--The 3 in. pin would flare a little less, so you would create more motion at the breakpoint, while the 4.5 would flare more earlier to give it more of a forward roll at the breakpoint. Simply, if you want more reaction down the lane then go with the 3 in. pin. Hope this helps.
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My ball won't hook- Heck who am I kidding--It never does!!