Thanks, T Fox. We are pretty sure it's a spine issue. The arrows are 29" long and have 100 grain tips. This Vapor brand is one I'm not familiar with - an economy brand that they sell at the local archery shop - but if the "4000" designation is the same as Easton's spine charts for a "400" series, then it looks like the arrow may need so be a little stiffer. Torque isn't a problem for this shooter, I'm pretty sure. He shoots with an open hand a lets the bow sling catch the bow. We will have the pro shop check the idler cam. He doesn't want to go down on pull weight.