Sorry for bringing up an old post, but I was wondering where you saw the 1.5x expansion diameter requirement for FBI testing protocols? I've been trying to find it and, as far as I can tell, there is no specific expansion diameter requirement. From what I've seen and read, the goal is penetration depth of 12" to 18" and positive expansion. (
CALIBERS -- FBI Ballistic Test Protocol)
I'm no ammo expert, but IMHO, there's always going to be a trade off. You either get more expansion or more penetration. Factors involved in each deal with bullet weight, velocity, design and frontal cross section. Generally, factors that increase penetration include heavier weight, slower bullets, thicker jackets and a narrower frontal cross section. That's why rounds like the Federal HST, which wow most shooters with it's incredible expansion, tends to be on the shallower end of penetration. (
http://le.atk.com/pdf/SacramentoCountyWBW.pdf)
Additionally, I seldom care about the diameter of the recovered bullet. What I'm interested in is the wound track between 2" and 7" of penetration. That's when the bullet is at full expansion and cutting tissue as it passes through. Once the petals have been fully peeled back, it's pretty much making a relatively narrow track that closes back down to original bullet diameter.
I think that's where manufacturer tries to find a delicate balance between expansion rate and penetration. When you throw a hollow point round with a thin jacket near the ogive and push it out at +p velocity, you have a tremendous expansion rate once it enters tissue. But the trade off is that you get the parachute effect; where the frontal cross section is enlarged to such a degree so shortly after penetration that overall depth suffers from drag and deceleration. Sure, a heavier bullet can help with that problem, but it won't make it go away.
Anyways, regarding Critical Defense vs. Critical Duty, I think the two rounds are entirely different animals. I don't think I would ever use Critical Defense for any purpose because of it's marginal penetration. While the Critical Duty bullet doesn't look impressive when it's been recovered, take a look at the wound track in gelatin, especially the first few inches. When you combine that with their increased penetration depth, I think it's a very formidable round. Add in it's ability to defeat hard obstacles and it's probably what I would use if I were a LEO. While it's probably not the ideal carry load for the average Joe, based on the FBI's current choice, the Winchester PDX-1, I really think that Critical Duty is a strong candidate for law enforcement...
