The Electricity in the bullet stuns the victom for a long amount of time. The downside to this is that the reload rate is slow and only one bullet can be in the chamber at a time. In addition to creating the electric charge, the bullets also are slow
The stun rifle modification was developed in order to increase accuracy of the modern rifle. With the modification, the rifle's base accuracy is 90%. An added side effect is that since the bullet travels through the tube, it gets charged with electricity.