There is a quite famous scene in the original movie where Robocop comes up to a guy, grabs barrel of his automatic gun and bends it downwards, while the guy continues holding the gun in shock. Isn't that completely impossible and the gun would've got torn out of his hands with the force needed to bend a steel barrel?
Depends on the state of barrel, it's temperature, the thickness, any defects. The barrel of the Sterling Mark 6 Submachine Gun seems fairly small, with thin walls. The crimp shows it was compromised right past his hand. It's obviously an aluminum movie prop.
Physics requires the the strength exerted on one end of the barrel or tube to be equally exerted on the other end for it to bend. Since it bent past his hand and not in it, the other end of the barrel (aka the rest of the gun) has to match the force. Realistically, no, he would not be able to hold on without at least some sort of show of force. He's basically passive. Myth Busted.
He could bend the barrel. But even so, if he grabbed the barrel and tried to hunch it down, the weapon would pivot barrel down unless the assailant had a grip like a vice. Robocop had no leverage what so ever to bend the barrel. steel used in a simple 9mm barrel has a elastic modulus of 190-200 gigapascals, You could bend it but you need leverage.