My understanding is that the M turret is a hybrid with the thinner front cheek armor of the initial T-72 model 1975 but the laser rangefinder of the T-72M1 in place of the coincidence rangefinder. An ID feature between the two is the M1 has a step at the lower front edge of the cheek armor right below the smoke grenade launcher conduits while the M does not.
M1 upper photos, M lower photos
