There are 2 most prominent concept in WBB hopup. The first one is the older and more well known concept of rotating the gel by creating a different air pressure which is what ATK hopup are made off. They usually came with a small hole which displace the air as the gel passes through, creating the magnus effect in the process. Alteration of air flow is a delicate process, while it creates the spin, the spin are usually inconsistent, hence lead to gel projectile to spread very wide. This type of hopup are usually plug and play since there is nothing much to tune.
The second concept which is something similar to the airsoft hopup but instead of having the hopup at the start of the barrel, same as previous mentioned hopup, it sits at the end of the barrel as well. It creates hop by coming into contact with the water gel. While it create a much more consistent trajectory, it requires more tuning to get it right. Too much contact will caused overhopping, and in some cases, the water gel breaks before it leaves your muzzle. The best part is, you will be able to adjust the hop as a blaster with different barrel length, different spring power, different water gel will require a different hopup setting. Tuning might be frustrating, but once you got it right, it will work like charm.
DK hopup uses the second concept and this is designed for Lehui HK416A5 or Lehui HK416V2