i don't know exactly where the change is supposed to occur but in my 2-3/4" chambered guns 3-1/4 dram eq and 1-1/4 oz shot loads have to have the rings in the "light" configuration. i recall shooting some 3-3/4 1-1/4 loads long ago and i'm pretty sure i left the rings on the light setting for those as well but the gun may have functioned with the rings set on heavy with those. as long as i wasn't shooting 2-3/4" magnums i just set them on light and left them alone.