“Shooter” is the sort of action movie that excels in one respect, and one respect only: It recognizes from the very beginning that it isn’t, well, excellent. The film seems to understand that its viewers are primarily interested in seeing some combination of guns, explosions and Mark Wahlberg, and it dutifully sticks pretty much to those three categories. That the movie at least knows its limitations should be enough to distinguish it from most other items in the late-night TNT lineup, for which it is surely destined.

Various critics have puzzled over the question of why Wahlberg is so consistently effective in supporting roles and yet still fails to land a major success as a marquee actor. Whatever the problem is, it isn’t Wahlberg’s acting chops. Playing the lethal ex-Marine sniper Bob Lee Swagger, Wahlberg manages to achieve a formidable screen presence in “Shooter” that is at once stoical, wry and understated. Few other living actors are capable of saying lines like “Welcome to Tennessee, the patron state of shooting stuff,” and making them sound so cool.

But “Shooter” finds a good lead actor languishing in an otherwise forgettable film. Besides Wahlberg, the film’s one saving grace is that it’s driven by an internal logic that is both consistent enough and absurd enough to be reasonably entertaining. According to that logic, one properly pissed-off soldier is capable of obliterating an entire platoon with homemade weapons, the Attorney General drops f-bombs like there’s no tomorrow and even the zaniest conspiracy theories prove true. In one scene, a decrepit old codger (played by aging musician Levon Helm) mentions offhand that the additional gunmen from the Kennedy assassination were actually buried in the desert. Asked how he knows, he replies, “I’ve still got the shovel.”

Such is the outlandish nature of the universe in which “Shooter” unfolds. The film opens to find a retired Swagger passing a life of solitude in the Rocky Mountains, only to be importuned by a shadowy government official (Danny Glover, sounding as if he were wearing permanent headgear) and his stooges for a top-secret mission. According to recent intelligence, it seems, the President will be targeted for assassination, and the government needs Swagger’s help to figure out how the sniper will execute his job.

Swagger begrudgingly agrees, only to find himself quickly dragged into a whirlwind conspiracy in which he is framed for the murder of an African dignitary. With just about every government agency soon bearing down on him, Swagger decides to turn and fight his way to justice by tackling the conspiracy head-on — employing, of course, a truly terrifying arsenal of firearms, makeshift explosives and cutthroat commando know-how along the way.

The ensuing 90 minutes deliver the obligatory multitude of deaths and detonations, churned out with unflagging intensity. Swagger manages to enlist the help of a skeptical FBI field agent named Nick Memphis (Michael Pena) and a svelte brunette (Kate Mara), and from there it’s off to the races. Any viewer who actually attempts to unravel the film’s principal subplots — say, how Memphis discovers Swagger is innocent, or how the whole conspiracy against Swagger really works — is bound to become confused or, worse yet, dreadfully bored.

Indeed, at its core, “Shooter” is relatively formulaic endeavor whose cynical, postmodern notions of conspiracy aren’t even provocative enough to distract from its glaring cliches. (Apparently, any movie featuring dialogue between two government agents must contain the line, “You’re asking questions that are way out of your pay grade.” “Shooter” makes no attempt to buck this trend.) For all its truly impressive action sequences, the movie is propelled by plot devices of profound mediocrity: In one scene, the evil senator (Ned Beatty) reveals his arch-strategy to Swagger with a dastardly grin, while in another the cabal of villains sit around smoking cigars and congratulate one another on their treacherous triumphs.

“Shooter” is best enjoyed as a hagiography to Wahlberg’s masculinity, rather than a suspense film of any substance or coherence. Those who wish to see Swagger jury-rig an IV in his bicep with a marinating needle, or use a Poland Spring bottle as a silencer, or blast a can of Dinty Moore beef stew to smithereens, will come away satisfied. And — as if the movie weren’t already coursing with Wahlberg’s testosterone — there’s also a slow-motion shot of Swagger, set against an American flag background, that’s got to be a good 10 seconds long.

Maybe someday Wahlberg will get the starring role he really deserves. For now, he’s got to settle for making movies like “Shooter.” Such movies may not generate many complaints, but they’re not worthy of very much praise, either.