weapon swapping issues.

so as i have recently learned theres a mechanic in bs2 called weapon swapping. and as such i tried it and i cant get it to work for the life of me. for example say i have three turns. first two turns i normal attack with jubjubs bow and then last turn i swap to deep sea anchor too get a 200% procent attack bonus. so i do one normal attack with that weapon to end my turn. so when it then attacks its just three hits with the deep sea anchor instead of the bow. so whats going on here? ps: sorry for the bad hand writing and if theres additional info needed like a video to show it ill be sure to send that