The Kimber Warrior appears in-game as the "1911". It incorrectly holds 10 rounds in its magazine; its real-world counterpart only holds 8 rounds in the magazine.
The SIG-Sauer P250 Compact appears in-game as the "P-9mm". Just like in the first game, it is incorrectly described as being Austrian, and holds 17 rounds in its magazine. It is erroneously the standard-issue duty pistol of the San Francisco Police Department and the Oakland Police Department, the former issues the SIG-Sauer P226 and P229 in .40 S&W while the latter uses the Glock 17.
The Saiga 12K appears in-game as the "SGR-12". It has a custom buttstock, pistol grip, and railed handguard. It is used by SFPD SWAT, which isn't actually outside the realm of possibility as some American law enforcement agencies do have Saiga and VEPR shotguns in their inventories.
The custom AK-103 from Far Cry 3 & Far Cry 4, as well as the previous game, returns as the "AK-47". Is dual-wielded by Devon von Devon (Jimmy Siska) in the trailer of the fictional movie "Cyberdrive".
The Patriot Ordnance Factory P416 appears in-game as the "Goblin". It uses the same model from the previous game, which itself originates from Far Cry 3, despite its name referring to its depiction in Ghost Recon: Future Soldier. It is used as standard-issue rifle of the SFPD SWAT, a somewhat odd choice outside of the world of Ubisoft-isms.
The SVD Dragunov from the first game, with its Far Cry 3 ultra-shortened barrel, later production skeletonized synthetic stock, compressed receiver (hybrid with Ghost Recon: Future Soldier's PSL-54C), and Belarusian Zenit 8x42 POSP scope reticle, reappears in Watch_Dogs 2 as the "SVD". It is incorrectly used by SFPD and Oakland PD snipers.
3D-printed guns are featured. While this is possible in real life, real home-made 3D-printed guns are quite fragile; thus, they are restricted to very simple designs, or require incredibly expensive equipment such as laser-sintered metal deposition machines that cost a minimum of half a million dollars, vastly more than the traditional tools needed to stamp or machine firearm parts. In essence this game uses 3D printers as if they are Star Trek replicators, much as "nanotechnology" was used in older near-future sci-fi (and before that "robots" and then the more traditional "magic"). Some of them, also feature "smart bullets" that "autohack" their targets, which would be impossible with 2016 technology (or at least impossibly expensive). The 3D-printed guns in-game are more or less just normal firearms.
Handguns
"4N00bs Pistol"
The "4N00bs Pistol" is based off of the Kimber Warrior, and is in fact just a slightly modified model of the game's "1911".
The "Bullet Hell Shotgun" is based off the the Benelli M4 Super 90, with a skeletonized stock and pistol grip, and with a handguard resembling that of a typical pump-action shotgun's pump.
The "DDoS Shotgun is also based off the Benelli M4 Super 90, with what appears to be a skeletonized collapsible stock and pistol grip, railed handguard, and is fitted with a box magazine.
The "Goodbye, World Shotgun" is once again based off of the Benelli M4 Super 90, this time with a pistol-grip only stock, and using a drum magazine. The handguard appears to be based off of the heatshield on the Franchi SPAS-12
As an interesting note, all 3D-Printed sniper rifles in Watch Dogs 2 are covered in spikes, most notably on the cheekrest. This would obviously prevent the cheekrest from being used safely--the recoil from firing would potentially cause severe trauma. However, the spikes do not have any impact on gameplay, and were likely added to make the 3D-printed snipers more visually distinct.
