QUOTE (Night Train @ Aug 9 2008, 02:53 PM)

IIRC
The gas is meant to shield and cool the weld but in gasless the mig wire has a flux core so it produces its own shielding gas as it melts. The benefit is that it is a simple point and squirt welding tool, like a stick welder but without the 'stick' getting shorter. It is also able to weld thin sheets better then a stick welder. The downside is that the welds are not cooled as there is no gas flow and the welds may not be as nice or as strong depending on wire and metal. It also means that it can't weld other metals as flux core wires are not available in many grades and without gas it means ali welding is out too.
However, gasless mig is a good point and squirt, get you out of trouble, tool for simple jobs without the need for a tiny and costly bottle of gas or a huge and heavy grown up gas cylinder.
be very careful of the fumes given off using these,i seem to think flux cored wire has been banned in the states because of this.