The Todd Jarrett grip
Captain of a Crew of One has an excellent visual depiction of the hold that Todd Jarrett teaches at Blackwater. It's not Weaver, more Isoceles, and involves a more extensive weak hand grip over the strong hand. Considering that he's the world's practical pistol champion, there is much to be said for it.
He taught it effectively, by forming our hands into the grip and then marking X on them, so that each hand had half the X. Then he'd show how you were unconsciously going back to Weaver, or letting the grip slip when firing a string.