JP Carriers?

[LRRPF52]

The bearing surfaces of a carrier are in 4 locations and are the widest portions sectionally of the AR15 carrier. There are the only real places where the carrier contacts the Inner Diameter of the upper receiver, which needs to be hard coat anodized with a Type III process, then have a dry film lubricant applied to it if you're following the TDP that the military guns use.

I think JP just increased the surface area of those rails on the carrier.