As I reported the other day:
I have lots of one fired brass but I knew that brass wouldn’t chamber in any some other rifles even though I was using a full length resizing die. I got my hands on a .300 Win Mag rifle that had problems chambering it. Then with a few rounds of empty, once-fired, brass, my micrometer, and the specs for the brass I sorted out the problem. I found the case just forward of the belt was one to two thousands of an inch larger in diameter than spec. I think the die is the problem so I ordered a new resizing die from a different manufacture and which I expect will fix the problem.
The new die arrived yesterday. It does fix the problem, but just barely. The specification for the case dimension in question is 0.513 inches. The once fired cases were 0.514” –> 0.515”. After going through the new die they are about 0.5135. The brass chambers, but it is tight. I ordering still another die.
Update: I looked up the SAAMI specs on the cartridge and chamber rather than what the reloading manuals tell me.
The portion in question of the case is specified as 0.5126”. The chamber is specified as 0.5136”. I suspect the rifle in question is at exactly the minimum specification while the dies, combined with the “spring-back” of the brass being used results in something oversized. I ordered an RCBS undersized die which should solve the problem.
Update 2: Thanks to an email from Bob B. I ordered what looks like a better solution. The Belted Magnum Collet Resizing Die. I canceled the order for the RCBS undersized die.