Have been running the recommended 3/4" ESO but sometimes decreased to 1/2"

Innershield Experts: I am running a Lincoln DC-600 with 5/64" Dia NR-212 wire at 18 Arc V and 75 in/min wire speed welding 1/2" HRS to 3/4". 95% of the time the welds look great....but then the wire wire "stubs" and spatters and jumps and it is hard to get a good looking wel...