Need help on Caspian factory rust inhibitor coating removal

There is a rust inhibitor coating on the frame and slide from Caspian. Called Walt from caspian and he said that hot soap and water would remove the coating. Tried that and it did not work. Tried Mineral Spirits, Acetone and Dawn with no luck. What does work?

Thanks

Mark

bead blasting?

I leave it on while fitting the gun.. once done normal finishing will removing it..sanding/polishing or bead blasting depending upon the finish.