Surveillance footage of the shooting shows Jeffrey Alan Williamson in a blue T-shirt holding the door shut, so the robbers couldn't get out.
One robber tried to kick the door open, but when that didn't work, the other suspect shot at the Good Samaritan in the shoulder.
Williamson said he was just trying to do the right thing.
"The objective was to get him out of there as quick as I could. So with four to six people in there with him behind the counter, the objective was not to cause a problem with all the people. He could have shot everybody," he said.
The search for the suspects continues. Meantime, Williamson was treated at an area hospital and released.
Workers said the robbers have targeted the convenience store five times in the last seven months.