You absolutely have to make the effort to use the same grip tension irrespective of the position/rest you are using. You don't want to hold the revolver differently offhand than you did when you sighted it in off the bench.

This is an instructional video I did for Gun Digest TV, that explains the method I use. It may not work for you, but you need to experiment and come up with a method that will work for you.

https://www.youtube.com/watch?v=U8ZC_AB7n_Q
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Max Prasac

Semper Fidelis

Bovine Bullet Test https://www.youtube.com/watch?v=mmtZky8T7-k&t=35s

Gun Digest TV's Modern Shooter: https://www.youtube.com/watch?v=nGo-KMpXPpA&t=7s