Most flux core wires that are designed to use with shielding gas are formulated to use with CO2, or 75% Ar, 25% CO2. The operating characteristics, such as splatter, slag removal, etc. are more dependant on the slag chemistry than shieling gas. For instance, a E71T-1 FCAW wire with an acid slag can run in spray mode with 100% CO2, and have no splatter at all, be self slagging, and have beautiful looking beads, while an E71T-5 electrode with a basic slag can run globular with 100% CO2, and have lots of splatter and hard to remove slag, with rough looking beads, but you might need to use it for the better properties. Of course not all E71T-1 wires run good, and not all E71T-5 wires run bad, it greatly depends on the manufacturers specific flux fomula. The advantages of flux core with CO2 over self-shielding, is more consistant weld metal properties, and less fumes/smoke. Disadvantages are you have to have a bottle with you, and it's no good in a draft.