The difference betwen equal weights of Lead vs Bismuth is the height of the shot column and amount of surface area in contact with the bore. 29gr of 7625 is 29gr of 7625. With the lead load you generating 5900 PSI. Nice shot has the same size shot column as lead, but because it's harder than lead it generates more pressure as it has a harder time squeezing down through the forcing cone. This puts you up around 7400 psi with a fold crimp. Using a roll crimp will drop pressure, maybe 600, maybe 800 maybe even a 1000. Only testing will tell for sure. I would stay with the low pressure lead load and add 1500 psi. I can't imagine a sound Parker 10ga having an issue with an 8000 psi load. If you go too low you risk bloopers, especially in cold weather.
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