I have a lincoln 140c and used 308L .023 wire with C25/75 gas. Mig with C25/75 is not ideal, stainless is totally different than mild, but the welds are holding up and aren't rusting. Expect lots of spatter and welds that will look like crap. Definitely practice first, SS really surprised the heck out of me when i first worked on it. With the 140C i think i cranked the voltage to max(j) and used wirespeed 5-6. You need to have gas, otherwise your welds will look like a sponge.
I got this from a welding forum and a guy referenced lincoln's website:
"The shielding gas recommended for short-circuiting welding of stainless-steel contains 90% helium, 7.5% argon, and 2.5% carbon dioxide. The gas gives the most desirable bead contour while keeping the CO2 level low enough so that it does not influence the corrosion resistance of the metal. High inductance in the output is beneficial when using this gas mixture.
Single-pass welds may also be made by using argon-CO2 gas. The CO2 in the shielding gas will affect the corrosion resistance of multipass welds made with short-circuiting transfer."
"Gases for pulsed arc welding are argon plus 1% oxygen, the same as used for spray arc welding."