Barbara Kopple’s engrossing, frustrating documentary “Gun Fight” — it’s not liable to inspire happy thoughts in people on either side of the gun-control debate — begins with eerie cellphone video footage taken during the Virginia Tech shootings in April 2007, and the aftermath of that rampage provides the film’s emotional ballast.

But events have rushed along since Virginia Tech, and Ms. Kopple has had to account for, among other developments, the Supreme Court decision last year in McDonald v. Chicago (a victory for gun-rights advocates) and the assassination attempt against Representative Gabrielle Giffords of Arizona in January. This leaves “Gun Fight,” which makes its debut Wednesday night on HBO, with a contingent, slightly queasy work-in-progress quality. The real question isn’t who’s right or wrong, but what’s next.

Ms. Kopple, who in the past has demonstrated her sympathies for labor unions (“Harlan County U.S.A.” and “American Dream,” both Oscar winners) and the Dixie Chicks (“Shut Up and Sing”), gives plenty of time in “Gun Fight” to people who believe that the limits on an American’s right to own and carry a gun should be few or none.