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BHN-18 is plenty hard enough for full magnum loads, but with lead bullets your gun's bore condition and chamber dimensions really have to be right in order to get good accuracy and avoid excess leading at full power. There are threads on the requirements you can search out. If you're not going for warm loads, but rather want to stay in the 1000 fps range that commercial lead bullets for this cartridge have, then you'll probably end up with about 7 grains of Unique or of Hodgdon Universal.
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