It's probably a good idea to measure the land to land bore diameter to see if the barrels are true .45's or closer to being .44's. But either way a starting .45 target load would be ~40 - 45 grains of powder. Then increase the powder charge in increments of 5 - 10 grains until the accuracy and power is satisfactory for the distance and the task, whether that's to punch paper or to hunt game with.
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