I am attempting to form 43 Spanish cases out of new Winchester 338 Win Mag cases by lathe turning off the belts, adding an E-clip to make the base flange work correctly through the gun, and fire forming them in the rifle. I am ending up with the necks too thick to load proper sized lead projectiles and need to somehow ream the necks down several thousandths of an inch. What tools might I use to perform this operation? I have both Pacific and Forster case trimmers.