Experts, I just bought an FX .25 tensioned barrel for my impact. I slugged the barrel to determine groove size. Does anyone know why the barrel groves appear to be .250 at the breach (lands) opening slightly larger through the middle to about 2" from the muzzle wherein the grooves appear to measure .2455. I believe I recall a conversation about the barrel being chocked. Do these measurements seem right? What diameter slug would you recommend I try first?