It happened around 4 p.m. at the store at 3247 Truxillo, near Tierwester.
Police say it began when two men, who were both armed, started arguing and then shot each other.
One of those men is in critical condition, but both are expected to recover.
The third man, a bystander in the store, was shot in the foot, according to officers on the scene.
Officials say they're still working to determine what charges the gunmen may face.