Worker Prophecy A Plunger Tube (Larger air volume)
Description states that it "can be used for Retaliator with some extra work". I don't know how much extra work that's referring to, but I had a devil of a time with it. Gave it a good solid go and chewed up a good Retaliator shell in the process.
I also have one of these in a Prophecy shell. It took a little finagling to get it to fit. (Phrasing.) Works like a dream, no issues.