Could we be talking about 2 different versions of S/A .303? The earlier stuff with the '60 & '61 "U" headstamps was cordite & corrosive, but I'm specifically referring to the OP's cases which are from the much later R1M3Z lots made in the late 70's & early 80's? That stuff definitely doeasn't strike me as corrosive because I've never had even a hint of trouble.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”