i have done a few guns and just left the engraving contrast with the black background. this is not tradition. most will cover the engraving with some form of colorant such as rustoleum paint. your gun is not pot metal. it is likely aluminum. best to use a lube for doing aluminum. i'm thinking...
around here, many are marking the v# on their catalytic converters. thieves see a cash cow stealing them and hauling them to junk yards. with a portable demo saw many are set free in less than a minute !
welcome to the forum. first-- u need 2 send a quality closeup of the tool u created. with such, we could show where u may have gone wrong. making yer own gravers is easy. but u need to know a basic geometry that u wish 2 make. just because it's a "v tool" does not mean it's correct for engraving.