Lead crushers and copper crushers are two different animals. The units do not convert well if at all, and neither is PSI.

Then we have dram eq., Tonnes, and all the various proof standards.

It can be disconcerting to wade through.

It's also pretty interesting, and part of the rich history of firearms development.

Keep at it.

"The price of good shotgunnery is constant practice" - Fred Kimble