The Cobra Assault Cannon is not the same as the Cobra Assault Cannon in RoboCop (1987). It is, in fact, an M-16 variant with an M-203 grenade launcher.
When RoboCop collapses on the ground from the grenade to the chest, the burn marks on his chest plate are nowhere to be seen.
As RoboCop collapses onto the ground after having a hole blown in his chest by Pudface, a black object can briefly be seen entering the frame right before RoboCop lands on it.