Pygmy, Same questions as above. Your HD SP gauge apparently measures from shoulder yet you mention Weatherby brass (belted magnum) the 338-06 is a non belted case (30-06). so, I'll assume the non-belted 30-06 case is HD spacing on shoulder. You say your fired case is LONGER than the Hd Sp gauge. Did you deprime the fired case before measuring ? This could very well be the reason your fired case measures longer. Remove the de-capping stem from the die & gently tap out the primer & re-measure.......... The best way to fire form is to seat the bullet to touch the lands so the cartridge doesn't rattle around in the chamber to the extent that the firing pin pushes the cartridge forward w/o ignition. The hd sp on unfired brass will vary a few thou. causing some to fire okay and others won't. Use the split case neck trick to establish bullet seating depth. Was your bolt also duracoated? Maybe some over spray in FP hole? How long since the bolt was diassembled & cleaned ? If the indent on the primer of the fired cases is visually deeper than the primer of the cases that didn't fire, seating bullets to the lands will probably solve your problem. Just a few ideas. Hope it helps :)