Harvester invincibility?

I went up against a Harvester 1 vs 1. I lost. With his shields down I dumped 3 mags of Xbow, 1 mag of senator, and 3/4 a mag of stalwart before his beam finally caught me. How did I not kill him? Did I just run into an invincible harvester or is there something else going on that I don't know about?

Edit: I aimed all shots at the eye on his head.

Edit 2: thanks for advise and info everyone!

I learned stalwart is too weak, xbow is weak against the head area and harvesters in general, the eye on the head is kinda a weak spot but it has lots of health so it's better to aim elsewhere, and the dark part of the upper leg is the weak spot, use atleast med pen against it.

Think I need a new load out. I like the xbow but I blow myself up more than I care to admit. And sometimes teammates too... Im only lvl 23 so I don't have that many great weapons ha. Been playing for less than a week 🙂