The Proton Pistol appears as a secondary weapon of Winston Zeddemore during the events of the Infestation. Winston has exclusive use of it because of the four Ghostbusters, he is the best shot, so he'd get the "precision" blaster.  It appears to be strapped to either leg during busts.
The Proton Pistol was first seen used by Winston against a Zombie near 20 Clinton Avenue. The Zombie absorbed the single stream and imploded. Winston also later pulled the Proton Pistol on Britt when she appeared to them in the Firehouse basement. Since then, it is usually equipped by Winston on cases. During the Fantastic Land case, Winston used the Pistol to shoot Peter Venkman while he was possessed by the Hungry Manitou, likely suffering some short term memory loss and violent bowel evacuation.
By the time of Winston and Tiyah Clarke's wedding, the Proton Pistol was yielded by Special Agent Melanie Ortiz. In the battle against The Sandman in a dream state, Winston visualized the Proton Pistol and opened fire with it.
- For Ghostbusters: Infestation, Editor Tom Waltz requested Winston use the Arm Mounted Proton Pack again. Erik Burnham misunderstood and it was referred to as 'pistol.' Artist Kyle Hotz then based the gun on the Proton Pistol from Extreme Ghostbusters. 
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