I am at about lvl 35+ guns expert still in act2, virtually all punks drop 15-shot automatic pistols.
Aside from those, I have found 3 revolvers (worthless IMO), one shotgun with maybe 15 rounds, one full-auto assault with 20 rounds, and two semi-auto assault rifles, each with 20 rounds. The punks occasionally drop pistol ammo, but I have not come across ANY shotgun or rifle ammo. I found a pistol ammo recipe, but no ammo recipes yet.
The shotgun I found was useless. The jury is out on the assault rifles because I have no ammo. The pistols are OK with a shock mod, but they take time, and ammo carry capacity is pretty low, even with the 3 ammo carry boost perks.