Maca if you dont have it "Shooting the British Double Rifle" by Graeme Wright 3rd Edition get it. It has regulation BP loads and nitro for black loads that will regulate in your double. I dicked around for years with my BP double rifle trying to regulate with BP. The powder available these days would not do it, used a Nitro for Black from his book and it was regulated in less than 20 rounds.PM me for more info.
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