I'm trying to fix a rail and bracket type of shelf this one to be precise.
Having a plasterboard wall, I picked self expanding nylon dowels like this.
My problem is, the rail being U shaped, as soon as I screw, the dowel is pulled out from the wall instead of expanding into it, as expected o_O How should I proceed.

vix. – yota Jul 26 '15 at 13:54