The fact that i have not tried engraving it bothers me. If anyone is willing to send me a scrap peice i could report back with my opinion and not heresay. A friend of mine is doing a knife build for me and it will have a nice big double guard and your right we are having a hard time finding 416. 303 no problem getting.
Doug, since this isn't a court of law I don't believe hearsay is a problem. The fact is most engravers who work on our knives won't cut 303, or if they will they charge more. As you push the line it work hardens, then tears out leaving a ragged cut. It takes extra time to clean up the cuts. On the other hand, 416 and 410 (along with most mild steels, 4130, and 4140) cut cleanly without the work hardening and tearing. Reliable sources include Ray Cover, Brian Hochstrat, Jim Small, Tim Adlam, and others that I know and work with. If they tell me not to make a fitting from 303 for them to engrave, I tend to listen to them.
In addition, 303 and 304 have somewhat similar compositions, but 303 is considered a free machining stainless. You'll find 304 to be gummy and a hard material from which to make fittings on knives. Just drilling a hole in it will twist off your drills. It's nasty stuff! On the other hand, 303 is fairly easy to work as fittings material. I've used it many times without any trouble. It's just not good for engraving.
Engraving 303 is a lot like engraving 6al4v titanium. It can be done, but you spend a lot more time either re-sharpening your gravers or cleaning up ragged cuts, or both.
David