Did you compress the powder?
Black MZ needs to be heavily compressed.
From the Alliant website:
Our experience through testing and hunting has been that best results are attained in the 50 caliber muzzleloader using 90 grains volumetric of Black MZ with sabot bullet weights of 240 grains to 260 grains. Good results with 300 grain sabot bullets were seen using between 100 grains and 120 grains volumetric of Black MZ.
Make sure that the barrel is clean and totally dry (swab barrel with dry patches until there is no evidence of moisture).
Black MZ functions best when heavily compressed by the seated sabot.
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