Burrowers is difficult to handle. I figured out I could throw grenades at them, but that seem kinda expensive.
I'm only at page 5 on Helldivers Mobilize warbond, but I can see that there's an assault rifle with medium armor penetration on page 6, so that's what I'm gonna work towards!
I'm using the R-63 Diligence, but that's not powerful enough. Only got light armor penetration.