Two times I took him down in one round.
1st time, I had a long running party that was just sick in AT Weapons and all had DEX of at least 30.
First four LAWs took him out and his return volley didn't do any damage my party couldn't shake off.
2nd time was my Super Loot Bag run, where I had everybody geared with a Red Ryder and Rifle skill.
Two shot kill. Return fire was negligible.
Then there was this one time I had to recopy Side 3 because I crashed the helo in the Citadel and couldn't make Cochise appear on the map. So I recopied Side 3 and, after finishing the game, went back to Vegas.
Totally forgot that the recopy would bring the Scorpitron back and encountered him with all Power Armor, 2 Ion Beamers, 3 Mason Cannons and still had ammo enough to spare.
I ripped a full Ion Beamer clip and killed him with one guy.
Long run characters beating him down with Proton Axes was fun.
First time I split the party and hit him from two directions was tough, but satisfying. He couldn't damage either party enough to even knock anyone unconscious, because he was splitting his attacks between the two. First time I didn't even have a character go UNC in combat with Scorpy.
Make the M19 an M14 analog. That's all I want. Swear to God.