There's really so much, and with the upcoming Bloody Harvest DLC finally detailed, we know even more guns are on the way. In the face of patch fixes and changes to the game, one thing that never changes is the plentiful supply of guns. Whether you earn them from side missions or they're dropped by a Maliwan soldier, you're rarely going to experience a shortage of loot.
So as you'd expect, Borderlands 3 keeps in line with this tradition and has even exceeded the number of guns available compared to previous games. If you're familiar with the Borderlands games, then you'll know that it always has an abundance of guns to collect.