As others have correctly stated you're going to want more than 10 gpa and higher pressure.   

Liberty is a "contact herbicide", this means that any growing point you want to kill you have to "contact" with a lethal dose of herbicide.    Pig weed species, especially bigger ones, can have a crap load of growing points.   If you want the plant to be dead dead, you have to kill every growing point.

15 gpa absolute minimum and 20 gpa is better.

With his yellow 8002 tips (assuming 20" spacing), 65 psi @ 5 mph would get pretty close to 15 gpa.         


IMO, if you want to do it right, you really need different tips.     Something like a Greenleaf TADF in either 025 or 03 size would be much better suited for what you want to do.   At ~$14/nozzle they're not cheap, but neither are weeds.