Since you are new to the game I'm going to explain why what you are looking for is kinda strange.
You are asking for a slag assault rifle with elemental effects. If someone is going to give you a slag assault rifle the elemental effect on it would be slag. It would have a percent chance to slag on it for how often slag would proc. The rifle's elemental effect would be slag and no other elemental effect would be with it. So whenever you get an elemental weapon it will be listed on the gun card and that would be the elemental effect. Only one weapon has 2 and that is the chulainn SMG which shoots slag and shock at the cost of slagging yourself.
What I'm trying to say is elemental weapons always have elemental effects. So in future reference if you talk about elemental weapons you don't have to ask for elemental effects. Topic title should be LF: slag assault rifle level 22, you don't have to ask for elemental effects.
Here is a little bit of extra info:
Fire weapons shoot fire, slag weapons shoot slag, corrosive weapons shoot corrosive, and shock shoots shock. Each weapon does bonus damage and works better on certain enemies it goes like this:
Yellow life bar means armored and corrosive works well on them Red life bar means flesh based and fire works well on them Blue bar is a shield and shock works well on them
Slags utility is to shoot an enemy until proc then switch to another non-slag weapon to do double damage on VHM and TVHM. Slagged enemies will receive damage on UVHM.
Explosive weapons are kinda all around good but slow bullet speed is a drawback. it can never hurt to have an explosive weapon in your arsenal for all around situational purposes. These shoot explosive rounds obviously. Only two enemies to my knowledge resist explosive and that is verm and assassin oney. --- They're not going to say no because of the implication.