My friend has a 300 win mag in a smith and wesson 1500. With this particular rifle, full length resizing dies don't seem to work. Brass from other sources that we run through the full length resizing die do not chamber in this rifle, but fit fine in other rifles. Went to new bulk remington brass, chambered fine, loaded and shot it, neck sized it, shot it again, neck sized again,etc... after the third firing there are nicks and gouges on the belt and the cartridge headstamp is starting to be obliterated. Is this a headspace problem. The loads are all well below max with either 190 or 200 grain btsp's. Rifle groups ok also. At a loss to figure out what's up with the brass. Anyone have theories or thoughts on this??please??