IIRC CO2 isn't recommended as a shielding gas for stainless as it can
compromise the corrosion resistance, as a purge gas it may be fine as
it's not exposed to the arc. I've known people that have used it for
steel body repairs and had good results but it's not as nice a weld and
more spatter apparently but has the advantage of better penetration, all
those I know who have used CO2 had mates down the pub that could get
bottles pinched as necessary at the time. The UK pub suppliers have
apparently clamped down on that as they can match CO2 consumption to the
drinks requiring it and flag up inconsistencies. The only time I have
tried Argon for steel MIG it didn't work well, the depot had no BOC
Argoshield light at the time and they thought Argon would do it OK but
didn't so later in the day they had Argoshield light back in stock and
swapped the bottle FOC and all was good again. I've MIG welded
stainless with 0.6mm and 1.0mm wire with the Argoshield light and all
went well. Argoshield light is apparently 93% Argon with 5% CO2 and 2%
O2, maybe not the best for stainless but it's what I have.