Dana, 304 is really, really gummy. Grabs and breaks drill bits and end mills to the point of great frustration.
303 makes great guard material as it is made with the addition of sulfur which makes for a "machine grade" austenitic steel.
"austenitic steel" means that is remains in the condition of austenite no matter what temp you take it to, so it's always non-magnetic.
Many, many makers have wrongly been taught that "300 stainless steels are no good.......". That is just utterly false.
It's just that everybody always confuses 303 with 304, which IS useless.
303 is one of the most non-corrosive of all the stainless steels.
However, it's more expensive than the readily available 304.
People who engrave hate 304 because it's so difficult to machine, so once again, "300 series stainless" steels get a bad wrap for knife makers.
303 is a FANTASTIC!! material for guards.
Like I said, it's also non-magnetic, which means that it can't be placed on a surface grinder magnet.
Those are some of the reasons why 416 has a good reputation, however, 416 does not come in dimensions often used by knife makers, which is FLAT.
But! 416 does come in every dimension of round stock from 1/32" up to about 8 inches in diameter.
Personally I buy round 416 stock, which is about as cheap as one can get, and then flatten it in my press and power hammer.
303 is great, but the addition of sulfur makes it a little pricey.
Online Metals has it.
Ain't knife making fun?