A wild guess is that the OP has a, "old school" chamber. o_O At the DATUM point .200" ahead of the bolt-face, all of the original Remington 6mm/ & 7mm BR brass, which I have & have had, feature diameters between 0.4635 and 0.4640" (same for the Rem. ,308 UBR - small primer full length .308)...