A couple of things....
One, my "beavertails" are as slim as I can make them while still filling the palm of my hand and offering heat protection. The wood along the top line is < 1/8" thick, so a lot of the time my fingers still wrap over the barrels a touch and I don't have such a solid grip on the wood alone as I might have with a beefier forend.
Two, I'm very conscientious about fitting them tightly. When I first completed the big 12 I had to drive a wooden wedge between the forend tip and barrels to get it off. That got old quick so I relieved the wood a little. Both the 16 and the 12 have suffered a little bluing loss from the friction fit, but I've seen no evidence they will ever loosen from a lot of shooting.
