RE: Why are slate calls round ?
It might be because the first slate calls were probably just a round piece of slate held in the hand, with no sounding chamber attached...The index finger and thumb would encircle the stone and the other fingers closed against your body to form the sounding chamber... At the first turkey seminar I ever attended, Dave Streb used several stones this way and made some good soft calls with them... That's just a guess on my part...As jalvja said, some slate calls are square or rectangular and probably other shapes too.. One famous example is the Lynch JET slate, which was a small rectangular slate call and was one of the few slate calls on the market in the 1960s when I started turkey hunting..