Steve peers through the door that separates him from Bucky, just in time to see Bucky's pistol run out of ammunition. Steve ducks back to avoid attracting the attention of the HYDRA agent and checks his own sidearm. There's a few bullets left, enough for Bucky to finish the guy off.

Steve hits the door control with his elbow and it slides open. He gestures with his pistol to Bucky, and then tosses it to him when he nods.