Ok, so I know it goes like this:

Acid for heavy armor
Fire for no armor(skin)
Shock for shields

But is explosive effective against anything special?

actually i have found explosives are good for vehicles and turrets as well as a good all aorund damage element.

with my blast rifle i can snipe a turret on my hunter.

well this saved me asking what the acid elemental dmg does (thankyou MoB), now all i need is a weapon which does corrosive damage so i can kill Moe & Morley

Explosive damage is good, for vehicles, turrets, and bosses. I dont use it though as I'd rather use shock and corrosive.

I think explosion is just your versatile, better than average for everything but not amazing element.

Im a huge fan of corrosive. I put it on my turret and the thing can wipe out anything in a few shots. Was level 35, killed 10 level 36 CL guys in one run. I was like DAMN. XD

quote TheBrapman

well this saved me asking what the acid elemental dmg does (thankyou MoB)

Dont mention it. ^^

The explosive element is just good for everything.

Although Corrosive is still my favorite. A good Corrosive weapon is well worth any cost.

Fire is and will always be my favorite. Shock is so pointless because I can take down someone's shields in 2 seconds anyway (except for boss fights, then it takes me 10 seconds). I don't use Corrosive that much because it doesn't do enough damage.

quote Darknet

I don't use Corrosive that much because it doesn't do enough damage.

I have a corrosive revolver that drops BadMutha Skags with no problem. I haven't seen anything that can last very long against it, but maybe that's just this revolver.

Actually, I found a use for shock.

The 1011 Eridian Lighting sniper rifle. It deals the most shock damage stack wise. I shot a BadMutha fire skag twice. Didnt do much. But the shcok effect killed it rapid quick.

I have that Iridian Rifle too! It's pretty sweet. Trying to raise my Iridian skill to see if it makes the weapons more useful. It's at 15 now and I still use my normal weapons more.

I also got this Iridian Shotgun which is pretty badass but needs to recharge often

Does anyone know where to get the Higher lvl elemental artifacts? I have lvl 1 explosion and Fire and LvL 2 Shock and Corrosion but how do I get lvl 3 or 4 and do they even exist?

Most of the higher level artifacts are found as rare drops from gaurdians or higher level quest rewards.

As far as elemental damage goes, you have no idea what you're missing until you play with Lilith. Kill something to activate phoenix and inflict fire damage, phasewalk to start off the shock, and exit with a corrosive artifact, and you're doing about 1000 damage or so a second(On my level 39 Lilith anyways). Anything that isn't dead in moments is usually so weak that you can clean them up with a few shots from the good 'ol SMG anyways.