In the tourist trap guide it says to bring 50 feathers and 3 bronze bars. When I did it I only used up 1 bronze bar and 10 feathers. The quest guide itself says in the items required 3 bronze bars and 50 feathers, yet the section about making the secret wepon says you need 2 bronze bars so both of those things are incorrect.

 

 

 

I know it doesnt count much as proof but I screenied and edited the final inventory to show the remaining bronze bars and feathers.

 

when i did the quest i found that sometimes when you tried to make the item it failed, and so needed to use another bronz bar ect so yeh, i hope that solves your answer.