Honestly, I've never filled either case with some substance, to see which holds more. I strongly suspect the 45 ACP holds more powder than the 10mm. I strongly suspect loaded to max levels the 45 would outperform the 10. Lots of variables to compensate for, but there it is.
The SAAMI spec on 45+P is 23,000psi. 10mm spec is 37,500psi. Good luck with your experiment. Let us know how it turns out...
