I was lucky many years ago that a good top taught me how to take a fist, at first was good but kind of pain full of course, then once i got used to it, the anal orgasm it gave me blew my mind, best feeling ever,
often to finish a good nights fucking with my wife and bi guys, after every one had empty balls, I would slide down on my wife's fist and wank my cock until i shot reams of cum over her face,
keep trying till you get way past the wrist in, you wont believe the feelings you get, my best is to the should orgasmic