I've done some searches and can't find the answer to this question. I'm loading for a 300 win mag and a 270 win with Norma brass and RCBS FL dies. The expander ball measures .3050" for the 300. I'm measuring neck tension by measuring the case mouth before and after seating the bullet. I'm getting .0020 to .0025 on both once fired brass and brass that has been fired 14 times and annealed 3 times. My gunsmith says that for my bolt action hunting rifle I need .004 to .005 to hold the bullet in place against accidental jars. What do y'all think is the proper amount of neck tension??? Thanks.