Beartooth Bullets are indeed heat-treated. We heat treat our bullets to a BHN 22, and over the course of 18 months they will age-soften to a BHN 21, where they will remain stabile indefinitely.
We have very carefully and intentionally chosen our alloy with a target BHN of 21 in mind. When heat-treated to BHN 22, the alloy only loses one BHN point when stored at normal room temperatures. This means that the load you work up today with our bullets will perform the same several years from now when stored under normal circumstances. Our bullets will not ever get softer than BHN 21, from aging or storage.
You will notice the Beartooth bullets are offered with sizing options. Marshall's technical book describes finding 0.002" over groove diameter to produce better accuracy than the standard 0.001" in revolvers, and shows an example table using his bullets. Many on the board find the same to be true in lever rifles (I've forgotten whether Marshall mentioned them in the book as well) regardless of alloy or who cast it? The point is, a little extra diameter covers the need to upset a bullet to obturate a bore. You just need to be sure your chamber throats are copacetic with that, and don't size the bullet down before it gets into the barrel.
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