There are tons of info on ballistic gel performance & penetration . I read some very intresting articles discussing f.b.i. test & what they demand from a bullet . They usually want around 11 to 15 inches of penetration . I'm a fan of 165gr ( hard to find ) out of my model 66 no dash . I've had problems & read info on the 125gr can damage the forcing cone & in my own experice locked the revolver up tight. Having stated all this I must say over penetration is my biggest fear in a defensive situation . So in my 44mag (Ruger redhawk ) I shoot 44 specials.