Actually, the Pro-Ears and Peltors use different types of circuitry, which is one of the reasons the Pro-Ears are more expensive. The Peltors clip the loud noise, i.e., they shut off completely when the threshold is reached. The Pro-Ears attenuate the loud noise, i.e., they lower the volume of the noise until it is below the threshold.
The result is that you can still hear noises with the Pro-Ears while gunfire is going on, just at a reduced level. With the Peltors, it is as if they are turned off completely during the instances of gun fire.