MIG welding stainless

Argon with 2% oxygen would make it wet out better, but straight argon will do. Helium adds heat, and you don't need extra heat when welding stainless because it is such a poor heat conductor.
Gary

I used a C25 (75%argon -25% CO2) on stainless before I decided to fork out some $$ for a new bottle and trimix 90%helium- 7.5%argon- 2.5% CO2) this try-mix is needed for shortcircuit stainless MIG. with 304 and 308 SS
you can use C25 but your weld bead will be more domed, and it will not flow (wet-in) in as nice as it would with trimix. also your weld bead will have a gray-ish look , and you will have more spatter.
lets recap C25= more domed bead, not wetting /flowing into the base gray looking bead more spatter
if you can live with it it will do the job.
also keep in mind they sell selfshielding stainlesswire which was designed to be used with C25.