The FBI suggests a minimum of 12 inches penetration in 10-percent ordnance gelatin for law enforcement ammunition. Penetration this deep is not hard to achieve with defensive handgun cartridges—until you also mandate the bullets expand, too. The more a bullet expands the less it penetrates. But, the more a bullet expands, the bigger the hole it makes. Defensive handgun ammunition engineers strive for an optimum balance between expansion and penetration.