I'm given to understand the OP isn't trying to erase a serial number or other ID to disguise a stolen gun. It's to simply remove a previous owner's initials.
I once bought a Baldor bench grinder upon which the previous owner had stamped, with full 3/8" high letter punches, his full name and complete social security number.
This was from back when people were told to engrave such things to expensive items like TVs and cameras, so they could be more positively identified if found at a pawnshop or the like. And obviously long before the SSN became such a crucial identifier.
On the gun, a 'smith I know had been brought a rifle receiver, a Ruger #1 falling block. A previous owner had electric-pencilled his name and the town he lived in on the side, in tall and kind of ragged letters. The gun was a legit purchase from a dealer, but the new owner didn't like the markings because it wasn't his name, nor was it his town, nor was it particularly good handwriting.
The 'smith simply surface ground the side of the receiver, a #1 is pretty slab-sided, and it was an easy job. Said it was about three thou to erase it entirely. Customer declined a full hot-blue, and so it was simply recolored with Casey's.
On curved surfaces, I'd use sandpaper backed with something like a flat hardwood stick, and slowly work the area in smooth strokes 'til the marks were gone. If you just try and slide the paper across with your thumb, you'll get undulations, and the fresh blue will look wavy.
I'd start with 320, kept lubed with a little WD-40, bump that up to 600, finish with 1,000, maybe bump up to 1,500 if it's a particularly glossy blue, and have the whole gun refinished by a reputable hot-bluer.
Or you can just buff it off there with those little sanding drums on a Dremel, and cover it up with some cold blue. Plenty of people have done that, too.
Doc.