It can be used on a .308 bit I think the BDC is calibrated for 5.56/.223
This optic is highly accurate on a .308. Manufacturer even clearly states that. The biggest question is are you going to get the most use from the BDC-6 reticle or the Hellfire reticle. That depends on what your weapon is going to be used mostly for. The optics is great on a .308 either way.
If the rifle has a picatinny rail, yes.