We've had this conversation before, but it is worth noting (again) that the "slap" method seems to be one which only has currency in the US. Here, and in Europe (including Britain) the ball and socket grip on the bolt knob seems to be the go. In fact in military training here the "palming" of the bolt was actively and vigorously discouraged.
You don't want a "death grip" though - the wrist in particular needs to flex, so that the opening and closing consists of two movements, not four: One more or less diagonally up and back, and one forward and down. You work it like you mean it. There's a lot less lost motion than with palming or the "slap" method. You see it in videos of Stanskyting competition, where often they'll also use another technique I learned as a kid: keeping hold of the bolt knob in the ball and socket grip and tripping the trigger with the middle finger each time the bolt locks closed.
I suppose the main thing though, regardless of which method you use, you need to practice it, so that it is a matter of muscle memory and so that you can do it reliably under pressure. No doubt you have seen many examples of people fumbling this under pressure, as I have, because they haven't practiced.
Here we are fortunate to have plenty of opportunities to practice. As well as service rifle competition, using bolt actions, which has such things as double snap and rapid serials (a lot of fun) we have lots of ferals, with no closed season and no bag limits. Knocking several pigs out of a mob before they make cover is a good test of how slick is your rifle handling. I've dropped as many as eight out of a mob, including stuffing additional rounds in as I ran to keep them in view.
