When Malone shoots Calvin, he uses a semi automatic pistol, which fires one bullet at a time. But when his bullet hits Calvin, there is not just one blood burst on his shirt, there are multiple squibs and blood packets bursts on his back as if he was hit by a blast from a shotgun.
During a scene in which Malone's vital statistics are displayed on a computer, his birthdate is shown to be July 12, 1939. However, his drivers license, featured in the end credits, shows a birthdate of February 14, 1941.
The sheriff looks at Malone's drivers license which clearly has a street address in Baltimore, then immediately asks "Why do you have a post office box for an address?"
A revolver with a silencer. Very unusual for a revolver. One such is the Russian made Nagant.