Lee- BobD is right using FFFFg as anything but pan powder is a definite no no, even if you never experience a catostrophic failure, you'll most certainly have dramatically accelerated barrel erosion and really horrendous fouling from the intense heat and pressure. And as you'll be so far beyond the FFFFgs' point of diminishing returns that you're velocity will be less than you'd achieve with proper BP grade. The accepted loading rules are based on very sound and well established principals.
fredj