Board Thread:General Discussion/@comment-25519625-20141106000307/@comment-3182180-20141106033730

In CSO, the Double Barrel and Dual Infinity are the weapons that the players can buy in shop to participate in their "upgrade event"s. They are sold in limited time and can only be upgraded at that time.

So for CSN:Z, I believe Nexon will release them later on for the same purpose, but I suppose they forgot to remove them from the Combat Blueprint. (these weapons are available back in CSO).