Quick draw reaction time: This is so much like the kendo myth from last week. And they're making the same misinterpretation, assuming it means that reacting is faster than initiating. In this case, the movie situation where the bad guy draws first and the good guy gets the shot first, the idea isn't that reaction time is always faster; the idea is that the good guy is more skilled, has faster reflexes, and is a bigger badass than the villain. It's always cooler to win when you're at a disadvantage.
Well, to be fair the "reality" of what's happening in the movie (good over evil) is different than the implication of what's happening. Pretty much all of the Hollywood myths they test can be waved away with saying, "You missed the point, the good guy's stunts ALWAYS work!"
Anyway I also noticed in the slow-mos of Kari's "faster reaction time" that it looks like she shoots the gun before it was fully pointed forward, I think a degree of accuracy needed to be put into this on if "getting the shot off first" would have even worked to take down the other guy.
The discrepancy between the Junior team's attempts working and Jamie/Adam's "real word" testing could be chalked up to the difference between reacting to a light simply coming on and reacting to a movement (which may be too subtle to notice quickly enough.)
I really don't think the "running out of bullets" thing needed to be tested. Not even in a "to prove the point to people" sort of way. I'd hope most people are smart enough to realize that guns don't come with a God Mode/Unlimited Ammo Cheat.