Leveling up your weapons in Black Ops Cold War Zombies can be one of the most painful processes in the entire game. However, there are several different methods that you can utilize to level up not just your weapons , but also your overall rank.
If you have played high rounds of Zombies and are not seeing any results in terms of weapon XP, then that's because as you reach higher rounds, the weapon XP bonus gets slower and slower. As you progress through to the high rounds, the overall XP is divided amongst all the zombies.
For example, let's say you are on round 1 and the max XP that you can get from round 1 is 1,000 XP. If six zombies spawn on round 1, that 1,000 XP will be divided among those six zombies, netting you around 167 XP per zombie killed. Compare that to reaching round 50 and having 100+ zombies spawning with a total of 1,000 XP divided among those 100+ zombies, you would get 10 XP or less per zombie killed.
Therefore, in Black Ops Cold War Zombies, reaching higher rounds does not benefit you when earning weapon XP. So how do you earn weapon XP fast in Zombies? The answer is simple: play only 5 rounds. That's right. You only need to play 5 rounds of Zombies, getting kills with the weapon you wish to rank up.
As mentioned above, you get XP faster as there are less number of Zombies, but more XP per kill. If you are ranking up your weapon from scratch (level 1), set it as your loadout weapon and spawn into Zombies with it. Play till round 5 using only the weapon you want to rank up and then exit the game. Start another game and repeat the process.
Here is our experience with a level 1 Bullfrog.
Note that the following test results were on Die Maschine Solo. If you party up with other players, you will get considerably more XP. Another thing to note here is that these tests were carried out during a 2XP (double XP) week. Even if it is not 2XP week, you will rank up your weapons much faster than your regular Multiplayer or Zombies game.
As you can see from the results above, just by playing five rounds in three games, you can rank up your weapon from level 1 to level 6. The best part about this is that each game takes around 6-7 minutes. So on average, you will spend around 19-20 minutes in total for three games. You can exit the game once you've completed round 5, and you won't lose any weapon XP. You will kill exactly 70 zombies in total by the end of round 5.
You will also notice that there is a considerable amount of XP gained in Rounds 2 and 3. This is because of the XP bonus that you get in these two rounds. We also recommend that when your weapon level reaches around 40, that you play three rounds instead of five.
This is because once your weapon reaches that high level, the XP gained after round 3 will have minimal significance. You can still carry on until the completion of Round 5 if you are willing to make use of every last bit of XP, but it will be a waste of time. You will earn more XP if you restart the game and complete three rounds instead.
You can make full use of this method by having two or more friends with you as it will give more XP. If you are a PlayStation player, you are in luck as partying up with other PlayStation players will give you another 25% XP boost.
This is one of the best methods to level up your weapons. You can also maximize this trick whenever double XP week goes live. You can also check out other methods to level up fast in Black Ops Cold War here.
Credits to Glitching Queen (on Youtube) for finding this.