«Three Spacemen Left to Die!» by Russ Winterbotham

Disease contaminated their ship; any moment one of them might become infected and spray lethal sparks to the others. There was no cure—except prevention. And that meant — Three Spacemen Left To Die!
Commander Al Andrews had closed and locked the energy-proof, neutralizing bulkheads against the creeping red glow that infected one quadrant of his circular space ship. Now he stood in the Control Center, in the mid-section of the revolving wagon-wheel ship, looking at Oakey Matthews.
There had been times aboard this ship when a whole crew had been comfortable in months-long trips through space. But now there were only three men, three men fleeing from death and it was no longer comfortable here, because death was breathing down the neck of at least one of them.
Oakey was intent on the instruments in front of him. Oakey was young, with a face that glowed with velvet skin. Even in space Oakey shaved every day, shined his shoes and pressed his uniform. Al was sloppy, bearded and ungroomed. But Al had lived most of his 50 years in space.
Oakey looked up toward Al. His young eyes searched the hard leathery face of his commander. He saw the grim set to Al's jaw and the hard lines around the older man's eyes. Al was cold. Nerveless as a piece of rope.
"How's Joe?" Oakey asked.
Al shook his head. "Last stages," he said. The commander went to a tier of built-in drawers across the room from the control panel. His arm reached out, pulled on the third drawer from the bottom. From this drawer he took an old-fashioned revolver and a box of shells. Not ordinary shells. The bullets were plastic, strong enough to pierce flesh, too soft to rupture the walls of the space ship.
"Don't do it, Al," Oakey said, watching the commander.
Al shook his head. He slipped bullets into the cylinder.