Joe,
If your receiver is NOT case colored, or has lost its original case coloring then a soft BRONZE bore brush and Hoppe's No. 9 may do the trick. The Bronze is softer than the best blued surface and will remove rust and oxidation without scratching or removing original rust bluing...but it is possible to put light scratches into case coloring if its been sealed with a varnish.
For your application, just wet the brush and work it in a light circular motion to clean out the engraving.

Roger

"I hate rude behavior in a man. I won't tolerate it" - Capt. Woodrow Call