PSA 18" Rifle-Length 6.5 Grendel 1:8 Stainless Steel 15" Lightweight Opinion?

[SDW]

The various SS alloys have varying degrees of rust resistance.
316 is very rust resistant. 304 is cheaper but will spot and rust slowly in a normal outdoor environment.
409 used in factory automotive exhaust will rust a lot quicker but still make the required longevity for warranty. And is cheaper than 304.
I haven't looked at 410 to 416 since it's not used in my industry or other hobbies.

I grew up in the desert so my rust prevention habits are very poor since it was almost a none problem in my youth.
I've had no issues with my 3 yr old SS 92FS with very little maintenance that's "indoors" most of the time but not sealed up or anything.

Takes me back to my first job, working for a Gov't contractor in the textiles industry (think backpacks and missile slings). In many cases the specs called for hardware made from "304 CRES". CRES being their abbreviation for Corrosion Resistant Steel.