The general common law rule followed in Arkansas is that the victim of an unlawful attack may defend himself with an amount of force proportional to the amount of force used against him. For example, while a gun can be used against a gun or knife wielding assailant, it cannot generally be used against an unarmed attacker.
Further, once your assailant breaks off his attack you lose your right of self defense and cannot hurt him additionally. You also generally have no right of self-defense if you are the “initial aggressor,” i.e. the first party to use unlawful force.
Additional rules apply when using deadly force in self-defense. Arkansas requires that a person retreat (provided he can safely do so) before defending himself with deadly force, though retreat is not required if the person is in his home. In addition, while reasonable non deadly force is allowed in defense of property, deadly force is allowed only in defense of persons. Arkansas also permits the use of deadly force to prevent the commission of a violent felony.
Also understand that the amount of force you are allowed to use in self-defense is the minimum necessary to stop the attack. So even when dealing with an armed attacker, if you can make him break off his attack without killing him you cannot do anything more.