One of the more interesting experiences I've had with the 165-grain Partition occurred when I used one of the late Verne Juenke's internal-concentricity bullet-testing machines for a couple of years, around 20 years ago. The machine used ultra-sound to test the consistency of jacket thickness in lead-cored bullets, and had a dial indicator to indicate how concentric each bullet was. It worked very well, and in fact a number of bullet companies used one to improve their manufacturing techniques--and some competitive shooters used them as well.
One thing I discovered during my experiments was that one particular lot of 165-grain Partitions tested just about as well as some "match" bullets. I then went back and looked through my handloading notes that that batch had grouped VERY well in every rifle I tried 'em in, whether a .300 Savage 99 or several .300 magnums, including a WSM, Winchester and Weatherby.
But other batches of 165 Partitions have tended to group better in milder .30s, especially .300 Savages, .308 Winchesters and .30-06s. My guess is they were more "average" in concentricity than that one lot--and since the milder rounds don't spin 'em as fast, that's why they tend to shoot better.
Sometimes I still miss having the Juenke machine, but the guy who loaned it to me was Dave Scovill, the long-time editor of Rifle and Handloader magazines. After two years he asked me to send it to Barnes Bullets, so I did. (This was something of a mystery, because the machine didn't work on monolithic bullets, whether copper or cast, because they don't have jackets. But I did as Dave asked.)
After my article on the machine appeared in Handloader, Verne said he'd build me one for a very favorable price--but unfortunately passed away before that occurred, in 2018. But if I did have one, would be tempted to ask you to send me a few of the 165s that shoot so well in you .300 WSM, just to see how well they test!
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