According to Sheriff of Baghdad:
There is no such thing. Your trigger finger is not strong enough. In this vid I pulled the trigger with this 1/2″ ratchet. Look how hard I hit the ratchet. I regularly break Glock triggers so I carry extras. Lol. Trigger jerk is actually #Anticipation. Anticipation starts in the brain and moves the gun before it goes off. Not your Finger!!! Commonly known as a flinch. The fix is relax the brain and Don’t Do It!