The rule of thumb regarding Nice Shot giving 1500 psi greater pressure than a lead load using the same components comes from the manufacturer.
From the blog on their webpage:
http://ecotungsten-niceshot.blogspot.com/"As for what sets Nice Shot above the other shot types is its ability to be used with older or finer shotguns, lead loading data and components as long as you stay 1500 psi under maximum pressure for the gauge you are loading for."
"Nice Shot is 10.2g/cc a little lighter than magnum lead shot as I stated in earlier posts. What is happening is Nice Shot being a bit harder 14~16 Brinell ( lead 11~13 ) when fired it does not absorb the energy of the acceleration like lead does. Thus causing a slight increase in pressure. This is why we recommend staying 1500 psi lower than the maximum allowable for the gauge you are loading for. And yes, other harder shot alloys will do the same."
I provided a link for the one published short ten load using Nice Shot. For some reason the Ecotungsten people go through Randy Wakeman to publish their loading data.
