Wargames Stuff:
Armour Thickness & Shot Penetration
Gunship helicopter Design System (incomplete, but worth looking at, I think)
Allied Stuff worth looking at:
BTRC's Guns, Guns, Guns (& More Guns) and the VDS. The first is a weapons design system giving real-world values for all sorts of firearms, including lasers and rail-guns for SF fans. The second looks at vehicle design for role-players, but again gives real-world figures. Check out BTRC.