Hey, Marine
I have always done my own engraving. Years ago I bought James Meek's book The Art of Engraving and learned a lot from it. More recently I got John Schippers' book, Engraving Historic Firearms, which I like better than Meek. I also have videos by Wallace Gusler and also Lynton McKenze. These are old enough they may not be available any more.
99.99% of any engraving you would do on a longrifle can be done with a square graver. They are easy to make from 1/8" X 1/8" O1 tool steel which I get from McMaster-Carr. Either of the books will show how to sharpen the graver. Get some brass practice plates ( I just use scrap sheet brass ) and practice, practice, practice. Hint: a straight line with uniform width is the hardest thing to accomplish.