It's paint, how about Paint Stripper?
Jasco makes a paint and epoxy stripper that pretty much dissolves anything. It's possible Taurus used an epoxy paint for durability. You may have to let it soak, scrape with a toothpick, reapply etc. but stripper will be better than acetone by itself.
Whatever you use, test a spot on the frame underneath the grip to see if it discolors the bluing. Good luck