If it is metal try automotive break-fluid.
Worked pretty well on my metal flash hiders and WA infinity outer barrel to remove the orange paint.
Pour some of it into a bucket, bowl or something like that and leave it there for a day or two. (Some people say couple hours is enough, but for me it only worked after few days)
I left mine soaked for few days and then I just used a rough sponge to remove the paint since it pretty much start to peal right off
But i am not sure this would work on plastic or damage the matte black finish beneath the slide.