No, you don't.
I could give you a picture of a cow, and someone could model it. They don't need to know how the cow works.
Yes, in that situation, if you asked someone to model a cow and not do anything, then fine, they can use just a picture.
But this gun shoots something or does something, (given that it's even a gun) which wasn't explained in the first post, which needs to be explained for people to make it properly.