+1 with the grouch. FSA and some other chainring designers use different tooth profiles and even the angles machined onto the faces of the teeth to ease the chain onto and off of the rings. You will not find these features on the inner ring but you may on the middle and outer. You can also look at the inner surface of the rings to find the pins that pick up the chain. The arc that the chain will make as it climbs these pins leads right into the short teeth.
These features are not commonly seen on older or less expensive (pre CNC Machine days) chainrings.