75/25 is the most common MIG gas for short circuit MIG. Straight argon is for TIG and aluminum MIG(spool gun most commonly). 6-10% CO2/argon is for spray transfer MIG, which is typically heavy duty production stuff(very uncommon for 'hobby' use). You can use straight CO2 for MIG also; little hotter, litle more penetration, little more spatter, but fully workable. Hobart makes an adapter kit for using paintball bottles w/MIG machines, which is nice for 'at track' repair/patch work. S/F....Ken M
