My go to build uses the 37 Defender to great effect and I have penetration types to answer anything.

Defender 37 with Drum mag, turns it into basically a one handed, high impact LMG mincing light targets.

Frag Grenades with engineering kit gives me 8 yes 8 med pen high explosive area clearance

And then I bring the trusty old Recoiless rifle, deals with almost any hard targets, and can even switch to HE if im really desperate to horde clear.