Originally posted by Big555 Again, I appreciate the responses, but if you paid attention to my posts I am not envisioning a big shoot out. I am merely asking if anyone has insight as too which caliber would be best suited to passing through windshields and possibly a vest while retaining stopping power. That's it. I don't want a third gun or second bug. I am looking for a single cartridge that would preform best.
How about a change in tactics and practicing for such an event? As JohnKSa pointed out, there are loads in every common service caliber to choose from here: http://www.ar15.com/ammo/project/Sel..._FAQ/index.htm
You might want to take the advice of Massad Ayoob and practice with your first shot placed Center of Mass with a follow up shot to the pelvic area just under vest level. If a perp were wearing a vest and didn't go down with the first shot CoM, that second round to the pelvis will at least take him off his feet. In your situation, I'd feel pretty comfortable with my 13+1 rounds of .45 ACP in the XDm 4.5, but since penetration after barrier testing was first conducted by the Texas DPS, you might want to take a page from their book and look into the .357 SIG. The load I use personally in .45 ACP is not on the FBI list for whatever reason, but in tests I've done shooting into water filled milk jugs, I get better penetration with excellent expansion with the Remington 185 gr. +P Golden Saber that has penetrated better than 230 gr. JHPs. And like the DPS, I believe in hedging all my bets first with shot placement, and by using a load that delivers 500 Ft/Lbs of KE into what I'm shooting at.