While we don’t have the historical documentation to prove it, it is quite unlikely that a nail gun was ever used in serious combat during the Cold War era. But Call of Duty says “screw it” (or “nail it,” rather) and adds the Nail Gun to Call of Duty: Black Ops Cold War and Warzone as a throwback to the DIY 11 Renovator nail gun in Black Ops III. While labeled as a Special Weapon, it acts a bit like an SMG, being an effective fully automatic weapon at close range. At long range, you might have to account for distance and lead your shots.
While you are able to unlock the Nail Gun by buying a Blueprint version of it in a Store bundle, you can also earn it by completing unlock challenges in Black Ops Cold War multiplayer, Zombies, and Warzone.
Multiplayer and Warzone Unlock Challenge
The multiplayer and Warzone challenge for unlocking the Nail Gun reads, “Get 5 Eliminations with Special Weapons in 15 different completed matches.” The other Special Weapons as of Season Four launch are the M79 grenade launcher, the R1 Shadowhunter crossbow, and the Ballistic Knife. While the latter two weapons are very competent in the right hands and can nab you that challenge, the M79 is great for taking on groups of enemies in matches with a high volume of players — just hope that not too many of them have Flak Jacket on.
Remember that the challenge needs you to kill five enemies in “different matches,” meaning reaching 10 or more kills in a single match will still only count as one notch towards the challenge.
Zombies Unlock Challenge
You can also unlock the Nail Gun through a Zombies-specific weapon challenge — the challenge reads, “In Outbreak, get 25 Kills with Special Weapons in 12 different completed regions.” A region in Outbreak is “completed” after finishing the main objective on the map, after which you can teleport to another named region through an anomaly. Consider “completed regions” to be each main session you have on any map. Again, the M79 is your best bet, since you’ll be able to train herds of zombies.