On the old barrels I practiced on, I used the Mig with 0.025 wire and tip. I have extensive experience with this setup welding light guage auto sheet metal up to chassis frames for old truck restorations. The gas I'm using is actually the reverse of usual. For some reason I ended up with a bottle of 75% Argon/ 25% CO-2. This will be done on a couple of AJ Aubrey sxs's I have. My practice barrels were on an old American Gun Co. wallhanger and it is now tight as a drum.