In case anyone came here looking for a solution like I did because the progress bar wouldn’t fill past 0% even after abandoning and re-accepting the quest several times, restarting the game, etc, I’ve got you. IGNORE THE TROGGS; I know they’re lit up and say they count, but trust me, I was bombing the bejeesus out of them and the bar stayed at 0% even though I was watching them die. No idea why it was doing this for me, but if you’re having the same problem, this is what I did:, Spam your #1 constantly; your hand will probably cramp (mine did, anyway)., SAVE YOUR #2 FOR THE ROWS OF MECHS. Any time you see rows of mechs lined up either stationary or walking, drop 2 on it, The bar fills REALLY slowly; it only filled for me when a mech died, which wasn’t every time I dropped the big bomb on them. I would say it went up 5-10% each full circuit around, so I probably had to go around the full circuit 15 to 20 times to complete the quest. Yeah. That many. And the circuit isn’t small, so it took forever.
Just be patient, spam the gun constantly, and only drop the bombs on the mechs. It’s slow-going, but you’ll get through it, just be patient. :)