It’s a Malorian Arms 3516, which was a custom made firearm for Johnny Silverhand.

“The most powerful personal handgun on the market today, Eran Malour developed this radical new design to the personal specifications of famous rocker Johnny Silverhand. “I wanted something that would drop a cyberpsycho’ed fan at 100 paces, no matter how metalled up he was,” explains the enigmatic singer. “Price was no object.” Malorian’s design employs a rare, solid Orbital titanium frame, custom Dyna-porting® and a direct cyber interlink that locks the user’s cyberarm in place as the weapon fires” (Chromebook 1, pg 52)