how do i develop a good sinker as a pitcher who throws over the top. To start, i grip the pitch whit my finger in 2 seam grip and i but my index next to my middle finger with pressure on my middle finger. any advice on what i should be doing is appreciated.

I dont think you can since you throw over the top. When you throw hard, does the tip of your fingers hurt/burn. Which ones and where?

Check this out

pretty interesting, and scientific, might help.

Yeah i guess you could say i throw 3/4 because i dont throw completely over the top. i get running action. And yes i developed a calause on my middle finger

where on the middle finger? tip or side?

its on the tip. i know i get good natural horizontal movement with my sinker grip, but my next goal is to make it sink as well