For silver/gold etc the normal HSS burrs are fine!
About steel, better ask the firearm engravers, I m just a bench Jeweller, working in softer metals!
Before remove metal on a real piece, try carefully out on practice pieces of the same metal!
Try out different speeds, more speed is not the better choice, the right speed is!
Often slower is better! High speed generates heat, the burr doesn't cut anymore it smears the metal, also burrs wear too fast!
Use a lubricant for the burrs/drills, like an oil, beeswax, or "stay sharp"!
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Burrs can hook, U damage the piece or even injure ur self!
Be careful !!!
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It might be also a good idea to check prices at dental tech. tool shops. Sometimes the same products are cheaper there than at Jewellery tool shops!
For drilling or burring/grinding in steel or other hardened metals. You need to use carbide burs. And always a slow speed. around 3000RPM is good. A lubricant will help to increase the life of your burs. If they get hot they get dull faster.
2.35mm burs is probably what will fit in your handpiece. But first check. 2.35 is the most common size for jewelers.
Busch has carbide burs. They have a yellow stripe on the shank.
Komet also has carbide burs. https://www.kometdental.de/en/Products.aspx