Sinker

[Booma]

I throw a sinking fastball but unfortunatly sometimes is sinks way out of the strikezone or doesnt move at all. i throw it using the "train tracks" with both index and middle fingers inside the seams, from an over hand angle. Is the a better way for me to hold this or should i just throw it and hope for the best?
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In the arsenal; 1. 4 seam, 2. 12-6 curveball 3.2 seam fastball 4. Valcun Change 5.The Knuckleball