Forget about using BP that has gotten wet. No good.
BP is a mechanical mixture of carbon, potassium nitrate, and sulfur.
After being thoroughly pulverized and mixed, it's formed into distinct kernels ("granulation") and packaged. Burning characteristics standardized.
Water dissolves the potassium nitrate and dissperses it. Mixture no good no more. Drying out removes most of the water, but the loss of proper mixture and granulation is gone.