The reason that a spear shaft is bent, can be attribuated to the fact that it has been standing, for example in a corner against a wall, for quite some time. I've seen this often.
I prefer to 'hang' my spears. There are two ways. Vertically by tying a piece of rope just beneath the spearhead and hanging it on a nail.
Or horizontally, by using several nails spread over the length of the shaft, depending on the weight of the piece.