How coincidental, I just bought a new Leupold scope for my newest AR15-guaranteed to deliver consistently repeatable accuracy at extreme distances and I purchased special hollow point ammunition with polymer tips that prevent clogging up when piercing thick or heavy clothing, like a hoodie for example.
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.