The greatest weapon known to man ; excluding nuclear weapons of course is the ADAMAS 275 Folding Combat knife...
In a protracted survival situation it is a 20 gauge shotgun, Remington 870 pump. plus the Remington 7615P pump rifle.
For concealed carry is the NAA 22 Magnum micro revolver : ) The big hitter revolver is the Taurus 410/44 Mag revolver and the Ruger SP101 38/357 revolvers.
For the greatest hand gun ever made is a no-contest the Sig Sauer P239 pistol in 9mm . . .
Any ammo must be 12 gauge or 20 gauge, 38 or 359 or 9mm. In a protracted emergency you need a commonly available ammunition supply chain ! ! !