Can't get this primer off!

I am trying to remove some old primer from some Intercessor torsos, but the stuff refuses to come off! I've soaked it for multiple days in everything from Simple Green to Isopro to Hand Sanitizer, and it still refuses to budge more than tiny incremental fractions at a time! Does anyone have any suggestions for how to remove this stuff? Its chaos black that I sprayed on about a year ago.