Over two hours of brainless action punctuated by even dumber dialogue, “The Expendables 3” tries to mix the old and the new with pretty humdrum results, perhaps because in order to avoid an R rating it keeps the carnage bloodless and the macho bickering decidedly mild.

The picture begins with a major set-piece—a prolonged sequence in which good-guy mercenary honcho Barney Ross (Sylvester Stallone, who also scripted with Creighton Rothenberger and Katrin Benedikt) leads most of what remains of his team—Lee Christmas (Jason Statham), Gunnar Jensen (Dolph Lundgren) and Toll Road (Randy Couture)—in a helicopter attack on a prison train to rescue his old Expendable mate Doctor Death (Wesley Snipes), who’s been held in captivity for eight years and is being transported to a hell-hole foreign prison. After being liberated, Doc takes charge of the train and rams it into the jail, blowing it to smithereens. His goal is obviously to kill the ruthless warden and his minions, but one must wonder about the other prisoners ensconced there—many of them presumably innocent—who must be blown to bits, too.

Any thought of that quickly passes, however, as Ross and the men are quickly off to Somalia at the behest of CIA bigwig Max Drummer (Harrison Ford), where they’ll join teammate Hale Caesar (Terry Crews) to capture an arms dealer trafficking in high-tech missiles. The mission goes awry, however, when the dealer turns out to be Barney’s old pal and co-founder of the Expendables, Conrad Stonebanks (Mel Gibson), who turned to the dark side and was wrongly believed to have died at Barney’s hand. Supremely cynical and confident about his operation, Stonebanks derails the mission and sends one of the Expendables to the hospital in critical condition.

That persuades Ross that his men are simply too old to keep putting themselves at risk, and he disbands the squad. But he still intends to go after Stonebanks with a younger crew he recruits with the help o mercenary head-hunter Bonaparte (Kelsey Grammer). The new quartet includes a former Navy SEAL named Smilee (Kellan Lutz), who’s good on a motorcycle; a highly-muscled sniper named Mars (Victor Ortiz); an ace computer hacker called Thorn (Glenn Powell); and Luna (Ronda Rousey), a martial arts specialist. Unfortunately this mission ends in disaster too, with Stonebanks taking the new team captive and daring Ross to come and save them. Naturally the oldsters insist on accompanying him; so too does Galgo (Antonio Banderas), a garrulous, hyperkinetic wannabe whose incessant stream of chatter is intended as comic relief (though at one point he pauses to relate the tragedy in his past that haunts him). They track Stonebanks to his base in a Middle Eastern country where he has total control of the national army and sends it against them. Much mayhem ensues as new and old Expendables unite to save one another and escape attacks by infantry and tanks, joined at the last minute not only by Drummer in his helicopter but by Trench (Arnold Schwarzenegger), Ross’s occasional helper, who wields a mean machine gun, and ex-Expendable Yin Yang (Jet Li, in what amounts to a cameo). Naturally it all ends in a final showdown between Barney and his erstwhile colleague Conrad.

It was probably inevitable that the franchise, which originated as a sort of goofball tribute to aging action stars, should have come down to a rivalry between the geriatric squad and a bunch of young whippersnappers, but frankly the new kids on the block are such a bland group that they’re barely identifiable from scene to scene. The banter among all the characters is hardly memorable either, and the screenplay certainly reaches its nadir in the ludicrously hackneyed speech in which Ross has to urge them to work together as a team if they’re going to survive—which should play as parody but doesn’t. (There’s some serious competition, however, in the attempt to craft one of those memorable catch-phrases for Ross in his face-off with Stonebanks, along the lines of “I’ll be back” or “Make my day.” It’s certain that what Stallone and his cohorts have come up with will not enjoy similar longevity.)

The cast seems to be mostly running on autopilot, with Stallone’s sluggish delivery casting a pall over the proceedings. Among the other Expendables, Statham shows the most energy, though Snipes has a few sly moments and Banderas obviously relishes going completely over the top, though to be honest his shtick quickly annoys the audience as much as it does his fellow soldiers-for-hire. Grammer is at ease in his seriocomic part, but Ford comes into his own only when he abandons a grumpy old man persona in the last reel, exhibiting a bit of his former wryness while piloting his helicopter as though Han Solo had come out of retirement to man the Millennium Falcon one last time. Then there’s Gibson, whose off-screen missteps have sidetracked his career of late. He’s actually pretty good as a bad-ass villain, spitting out his lines with a smug disdain that has a touch of genuine malevolence. It’s a turn unrelieved, however by even a hint of the dark humor that might have made the character really memorable.

Of course, acting is secondary to action in this sort of movie, and by and large the big set-pieces are okay, though so protracted that the excitement tends to dissipate and edited (by Sean Albertson and Paul Harb) without ideal crispness and clarity. Of course, the visual messiness is also due to Peter Menzies, Jr.’s busy but drab camerawork and Hughes’ sometimes manic, sometimes languid direction.

What “The Expendables 3” really lacks, though, is a bit a self-deprecation, an indication that Stallone and his cohorts realize that what they’re serving up is recycled hash from the 1980s. Instead they just play it straight, and as a result it comes across as a sad throwback in which the attempt to add some fresh blood is no more effective than a dose of Geritol. In the long epilogue at the close, Ford’s Drummer remarks that he hasn’t had so much fun in years. A pity a viewer can’t join in his enthusiasm.