There is nothing the standard AR will handle that I would consider a good long range round. Try stepping up to the .338 lupua or at the very least a 300 mag.
Funny you should say that, I’m getting a scope for my .300 win mag next. Still trying to pick one out. I have to admit though, I am a fan of the AR15 and the 5.56 mm round. It’s capable of a lot more than some people give it credit for. it isn’t a “long range” rifle/round, you’re right about that but at mid range, it’s plenty adequate.