I've recently come across this game, and am now playing through as Roland. Going for mostly shotguns, I found a perfect weapon for the cause - 56x7 damage, 5 rounds, 1.something rounds a second, accuracy 82. Was blowing off heads with it until it became clear the power was insufficient. So eventually I went through several assault rifles and machineguns, and eventually settled... on a revolver.
That has to be the single most broken weapon I've seen in this game. And I've seen a 890-damage airburst rocketlauncher, so that says something.
It doesn't quite one-shot Badass Lance Defenders, but can easily OHK normal ones with a well-placed headshot. Its only drawbacks are lack of a scope, and a 2-round drum, though it offsets the latter with a quick reload, and the former isn't much of a problem since the spread it does have ensures that, at the range you'd need a scope for, at least
some of the slugs hit the target. So that's that. Power of a shotgun, range of a sniper rifle, size of a pistol. To top it all off, with the flat 2-round drum it looks kinda like an old flintlock. Set me back 144K when I bought it, barely scraped that amount up. Love this thing to bits.