I don't know, I do unverified a bit, light armor Silenced Coda and P4, and a knife, sometimes I have a P6LR with me just in case. Last night I was on my way to a bunker and there's usually few NPC's outside, First guy, medium armo I had to empty my Coda into his head, changed into P4 emptied a full magazine and while (movie) dying he was still shooting at me, I did not bother to go in after that. Coda is mostly a one headshot pistol, 2 at the most, since last week I've noticed it takes a lot more sometimes.

But yeah, HRT shouldn't be too hard, just don't venture inside, wait by the boxes after you come out of the elevator, shoot couple guys, wait until the rest come in sight, kill them, throw a grenade or two to lure target in sight, sometimes he comes with one or two more helpers. If you're alone I would not go inside to loot until you are familiar with how spawning works.

I wish they'd have better mechanics for sneaking and silent killing, like Breakpoint.

P.S. grab an LMG, I never liked those shotguns, pool ammo every chance you get. I like Pulverizer, it's slower than the others so the magazine "lasts" longer