As I understand the MIG process difference between short circuit (globular transfer)and spray is more or less, you just keep cranking the amps till the wire no longer pulses. By pulses, I mean that this is where it contacts the weldment, melts the short wire section between the weldment and contact tip which turns to a molten globule that then transfer into the weld puddle due to polar attraction. In spray arc, the amps are so high that the wire becomes a constant arc and vaporizes into a spray that is transferred to the weld puddle which pretty much eliminates any possibility of cold lap and makes for a very smooth weld with very, very small ripples. Unfortunately, this is too many amps to run root passes with on open butt and without rolling it like a subarc, it is too hot to fill with. This then lead to the pulsed arc that can use higher current but still allow it to cool between pulses similar to the short circuit method (supposedly if you believe the hype from Miller and Lincoln)
