Pin length does not change the reaction. The pin location and the MB location do. They control the ball reaction, the reason saying the pin length will change reaction is due to layout problems.
As already mentioned a 2-3" is good pick, a dead on 3" is godly in options. Typically I order shorter pin length balls if I want a pin under drilling (early reaction) and if I want more of a snap and backend I go with something longer, more like a 4" and get it above the fingers.
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Just another aspiring junior bowler who hasn't hit full stride yet.