JHP ammunition adds 1 Extra Damage Roll (3d6 -> 4d6) but has -1 PEN.
Jacketed Hollow Point ammunition, or JHP, consists of a typical FMJ projectile which has had a cavity cut in the middle. Upon hitting a target, the projectile will expand and pieces of it will break off, generating greater tissue damage. The use of hollow point ammunition in armed conflict is a war crime.