Rocky Mountain Bully Bull Extreme Elk Grunt Tube - The all new, larger diameter mouth-opening and tapered venturi design of the Bully Bull Grunt Tube allows hunters to more easily obtain octave changes. Call is designed to be used with a diaphragm call and creates consistent airflow with the ideal amount of back pressure. Designed for use with diaphragm callNew larger diameter mouth-opening and tapered venturi designCreates consistent airflow with ideal back pressure