Most of the uber weapons you see posted on the forums are from folks who've gone past a certain level. In my experience I didn't get the uber drops until 30-something. In PT2 you'll definitely be coming across a lot of uber drops, so, I hope that answers you question. Oh, one more thing, it wouldn't hurt to play a co-op round with people, too. More people, better drops.

PT2 lvl 48 sledges shotgun FTW ;) not an uber weapon but still a good ole trusty shotty!

That 12x isn't a multiplier, it's the number of projectiles. You're only going to do 12x damage at extremely close range. And yeah, it's all about your level.

On PT2 do loot runs at the start of the Crimson Enclave I think it was. There are at least 3 guaranteed weapon chests and you can do the run in less than 5 minutes then just quit and repeat. That's how I got all my good weapons.

My best weapon on my playthrough was a shotgun that had an accuracy of around 75 to 80 percent so I could pretty much snipe with it almost.

Of course people also make their own über weapons

i got a shotgun that fired rockets 
 
that was pretty damn sweet

Hellfire Combustion SMG ftw.

" i got a shotgun that fired rockets  that was pretty damn sweet "