Here's some info from Game Informer about the different gun manufacturers and some of the differences in their weapons.
It's a fun (short) little read.
Highlights for me:
The bandits now make their own guns. "Instead of a scope, a Bandit sniper rifle might feature a glass bottle. Instead of iron sights, a screw."
Tediore brand weapons: "Once you’re done unloading a clip full of ammunition from this brand’s rifles, it can be thrown like a grenade. The more ammunition you have left in the clip when thrown, the more powerful the explosion will be. "