Depth of rifling, sharpness of lands and grooves, all wear differently. Even opposing pressures IE odds vs evens, can affect barrel life.
Rate of fire can afffect it but from what I"ve seen from lots of slow and medium fire vs uppers that were rapid fire, IE shot every second give or take, there was negligable life difference.
RE rifling, a single point cut tube will generally, on an AR in 223, outlast a buttoned tube by about 1500 plus rounds of difference.
of coruse I"m no scientist at all, just observations from what has to be almost a million rounds downrange knowledge from the AR
