At last count Gearbox declared over 17.5 million weapons in Borderlands. Now have your pick.
The weapons in Borderlands are incredible, and finding the same one twice is often a heavy chore. Each weapon has the chance to have explosive, caustic, incendiary or shock attacks. Weapons with these elemental abilities deal an extra amount of damage, and also have the chance to continually deal damage (I think the higher the multiplier, the better chance to light them on fire or corrode them...) to the enemy. Incendiary weapons are meant for flesh, shock for shields and caustic for armour.
It may not sound it, but the hardest thing about Borderlands is probably deciding on your weapons. At the start your backpack can only carry 12 items, so be prepared to compare guns stat by stat quite often. Considering you also need to carry class mods, shields and health packs, you will find yourself "full" nearly every adventure.
The guns in borderlands are divided into weapon types, these include: shotguns, pistols, combat rifles, snipers, sub machine guns, launchers and Eridian (alien) weapons. However, two guns being classified in the same group does not necessarily mean that they will perform in a similar way. For example, you can find a repeater (normal pistol) that shoots really fast, has a massive clip and has double melee damage, or a revolver that has just 2 bullets but insanely high damage, causes explosions as well as a scope for sniping. Each weapon class has it's ups and downs, and most have a corresponding character. During the loading screen, one line tips are present at the bottom. One of these tips states that each make/brand if gun is more likely to raise certain stats/elemental effects.
Atlas – best manufacturer, good all around.
Dahl – low recoil, decent damage.
Eridians – alien weaponry, high damage, unlimited (regenerating) ammo.
Hyperion – long range scopes, high accuracy.
Jakobs – high damage.
Mailwan – elemental damage (every weapon).
S&S munitions – extended magazines, elemental damage.
Tediore – fast reload.
Torgue – all round, not as good as Atlas.
Vladof – fast fire rate, extended magazines.
Gearbox – special easter egg items.
Now you’ve read this much about guns, so surely you want to know the coolest of them and what they do. Okay, so some weapons come with a “special effect”. Only a small amount of time will this effect be directly written (i.e +100% melee damage on the Clipper). A special effect will be written in red, and often funny or a quote from something. Another weapon with a special effect is Leviathan, which shoots rockets that arc rather than shoot straight. The result is a launcher that is harder to master, but can take out enemies behind cover.
Each weapon has a simple way of determining how rare it is, with 5 basic levels. White being the most common, then going through in the order, green, blue, purple and orange. I say 5 basic levels because the orange section is actually composed of 3 colours. Most people report finding 1 of the orange guns each play through, making the top tier (dark orange) very sought after.