ACR parts shared with M4 platform?

What parts other than the barrel are common between the ACR and the M4/M16 Family?

I have watched the animation on the Remington site and it looks like the trigger group and possibly the bolt are common.

Does anyone know?

trigger group, front sight post, magazine, extractor claw?

bolt is not common but it looks similar

Barrel is , well some are

Bolt isn’t no gas rings and tail is bigger