Flinch is a general term. I’m working on breaking down the different kinds of involuntary actions when shooting.
Take a look at Mel Gibson in lethal weapon shooting his Beretta and you’ll see a massive flinch. He blinks really hard. This is one thing that I consider a flinch. He’s only shooting blanks, I don’t want to see him doing live fire.
I also see a lot of shooters anticipate recoil pushing the gun down an instant before it goes off.
There is a an open and closed control loop description of what is going on. When we do things slow enough we can see what we’re doing and correct for them. When things happen really fast there isn’t enough time for us to adjust what our body is doing. Something that happens quicker than around .15 seconds is usually too fast to consciously react. The body’s nervous system sensing and controlling. For elite sprinters that start with the sound of a gun there is a minimum time after the shot of the gun that the sprinters have take to react. This is to eliminate anticipation of the sound.
Reaction time does a lot in flinching. Because the body can’t react fast enough our subconscious anticipates the recoil and starts to push the gun down.
Allowing the gun to recoil and the sights to rise is a good exercise. Group shooting is a drill to help. It also helps overall accuracy and form.
Putting on the gas flinch can start up again. This is where bill drills help. Bill drills into the berm can aid in relaxing.
Milking the shots. I see a lot of people shooting low and left, for right handed shooters low right for left handed. I believe it is called milking because the shooter is tensing up the whole shooting hand when triggering.