Okay, fixed the feats by dropping the flaw and going with this:
Hand Crossbow Mastery, TWF, Point Blank Shot, Weapon Focus (Light Mace), Rapid Shot, Precise Shot, Combat Reflexes, Woodland Archery, Improved Critical (Hand Crossbow), Lightning Mace, Improved Two Weapon Fighting, Improved Initiative, Greater Two Weapon Fighting, Blind Fighting, Crossbow Sniper
Okay, so that's a 30% chance to threaten, causing 2 extra attacks (but not any chance of 4 anymore). If I've got this right, each attack generates .6 new attacks, meaning the base attacks each generate .6+.6^2+.6^3... new attacks with no chance of going infinite, or roughly 1.5 extra attacks. Thus, with 48 base attacks we're looking at about 120 attacks, with roughly 34 confirmed critical hits, so by the end each shot is at +34 to hit and damage. Not bad.
Really, the trick here seems to be to get an attack routine that generates .99 attacks per attack, thus yielding a very long chain without going infinite. The original build was at 1.17, a bit too high because I somehow decided that 15-20 critical was 25%. The fixed build works, but it's lower than I wanted, so some work is needed.
Edit: Okay, if we use the original build, but just use regular Heavy Crossbows instead of Great Crossbows, and thus lower our critical chance to 20%, the magic number we hit is .78. This isn't perfect, but it's a lot better, yielding roughly 3.5 new attacks per base attack, or 214 attacks and roughly 41 confirmed critical hits. If we could somehow get a critical on a 16-20, yielding a 25% chance to critical as I originally thought, our magic number would be .975, which is as good as it gets. So the question is... how can we get a 16-20 critical threat range? And is it possible while still getting Time Stands Still and Raging Mongoose? If so, the number of shots would be insanely high without ever going infinite, which is my goal here.
JaronK