KenpoTex
Senior Master
This article is by Duane Thomas who interviewed ISPC/USPSA Grandmasters Brian Enos and Dave Sevigny about the proper way to execute the "thumbs forward" grip. This is the best analysis I've ever seen on each aspect of the grip. It's long, but worth the read.
http://www.handgunsmag.com/tactics_training/combatg_100306/index.html
http://www.handgunsmag.com/tactics_training/combatg_100306/index.html