The bungee type sling has issues. Yeah, it can stretch if you're trying to shoulder the rifle. If you're depending upon it to support the rifle while you're moving, the rifle will be like a pogo stick. Whacking you in many areas whilst bouncing about.
You generally don't attach a 2 point sling at the end of the receiver. However, there's all sorts of ways to rig slings.
Condor gear makes decent slings. Some of Blackhawks slings are OK also. It's a pity no one makes a DIY sling kit: about 10 feet of webbing and an assortment of hooks, quick releases and D or E rings or Chicago screws for terminations.