Agreed MtnHtr. One thing I’ve done that is similar is telling a shooter straight up that I am going to hand him the rifle back and it either will be loaded or not (or have him step away from the bench and look the other way while you work the action either chambering a round or putting the bolt over the top round with an empty chamber). The shooter won’t know and, in my experience, will work very hard not to flinch to avoid the stigma they feel about it. As you said, for the times that the rifle is unchambered, you will know one way or the other whether they are flinching. But this method, in my experience, can help to mitigate a flinch if it’s there as well.
