Code Geass has a unique Humongous Mecha in episode 8 called the Raikō that uses a massive railgun that fires shells that split into several dozen pellets, each "pellet" being roughly the size of a tennis ball.
Cowboy Bebop, episode "Gateway Shuffle": a group of insane ecoterrorists launches a large bomb toward a moon. As our heroes near it, it opens and releases three missiles. Two are destroyed by Spike, and just as he's about to destroy the third, it splits further into a thousand tiny rockets.
In Dragon Ball, Krillin uses a Ki Attack variation of this where he throws an energy ball into the air which then breaks apart raining death on all those below.
Mobile Suit Gundam SEED had various battleships and such that fired missiles into the air, which would then fire a rainfall of shrapnel to cover the enemies. It's been one of the most successful tatics for heroes and villains alike.
Full Metal Panic! pulled this off in The Second Raid season premier: when the Arbalest is retrieved by the Tuatha De Danaan, the sub fires several cluster missiles onto the tanks lining the riverside. The entire army gets wiped out in seconds.
Mobile Suit Gundam 00 Ali al-Saachez's custom Enact has a rifle attachment that launches a micromissile-launching missile.
Naruto has the Shuriken Shadow Clone Jutsu, which causes one throwing start to become a wide area cloud of them.
Banner of the Stars has antimatter mines that, when shot at by point defences, split into even more mines. These mines disguise themselves as the debris of the destroyed mine, and then jump any Abh spaceship that strays too close.
Transformers comic, Blustreak uses a missile like this as one of his signature weapons.
Iron Man: The Jericho missile at the beginning splits up and proceeds to simply level a small mountain.
The Avengers: A miniaturised version of the Jericho (from Iron Man) is shown as part of the suit's arsenal, used to take out multiple Chitauri.
Hawkeye also uses an arrow which embeds itself in one of the Chitauri and then releases a spray of projectiles into several others.
Star Trek The missiles of the Narada which break open and deploy warheads.
Spawn starts with Al performing an assassination with one of these.
Who Framed Roger Rabbit there was a cartoon gun that fired bullets modeled as western characters who then shot or otherwise killed their target with their own weaponry.
Night Watch the film Day Watch, there is an aluminum foil ball attached to a rubber band. If thrown, it unfolds in midair and splits into three identical, but faster and harder, balls, which also split, etc. It devastates Moscow in one strike.
In David Brin's Uplift series, some of the more advanced Galactic missles have multiple layers to them. In Startide Rising, the Soro fire missiles at a Synthian scout. He fires anti-missile missiles at them, and the missiles shoot them down with Beam Spam!
Dale Brown books since Fatal Terrain include the submunition-laden Wolverine cruise missiles. In addition, various UCAVs, although meant to resupply from a mothership and go for more attack runs, mount warheads of their own just in case.
In Banner of the Stars, the United Mankind develop a new type of mine (other sci-fi series would probably call them torpedoes), which can divide into four independent mines to overwhelm point defense guns or lie in wait in debris fields until a ship passes by. They're dealt with by deploying More Dakka.
In Harry Harrison's Northworld series, mention is made of shield penetrating bullets that hit a shield then fire another shot at the same now weakened spot, up to twice. note (original shot from gun, bullet hits shield and fires second, second hits shield and fires third.) This is probably also inspired by a Real Life weapon, the explosively formed penetrator.
In Harry Turtledove's Worldwar, cluster bombs are one of the modern-era weapons unleashed on World War II-era Earth by The Race. It takes a while for the contemporary soldiers to get used to them and several are crippled by bomblets blowing off one of their feet. Fortunately for humanity, they're also one of the weapons the Race only has a very limited supply of.
Thunder LRMs are essentially missile-deployed minefields, which even come in a variety of distinct types. FASCAM (see the Real Life section below) and cluster rounds for proper artillery weapons also exist.
Also, the Maximum Tech book introduced several types of specialized autocannon ammunition, one of which was a sub-munition round, which broke up after firing, like the special ammunition for the LB-X series of autocannons (Which were more like shotguns than autocannons.)
GURPS: Ultra-Tech has Smart Explosively Forged Projectiles that fly over the target before using the explosive force of the warhead to create a flaming armor piercing spike.
Star Fleet Battles drones (missiles) include multi-warhead capacity, such as Starfish drones and swordfish drones which fire a phaser at the target.
Transhuman Space has military spacecraft launching "Autonomous Kill Vehicles" (AKVs), which are basically robot fighters with guns installed — except that they also capable of ramming if the situation justifies it, bringing them into this category.
Warhammer 40,000 The Manticore Multiple Rocket Launcher has, as its most common armament, a rack of 4 (and only 4) Storm Eagle rockets. A Manticore may only fire one Storm Eagle per turn, and each Storm Eagle breaks into a barrage of 1-3 mini-rockets once the main Storm Eagle reaches the apex of its trajectory. Due to their temperamental nature, Manticores are sometimes distrusted by commanders, but having that kind of potential in firepower makes up for it.
Touhou: Fairly rare, but present. More common is mobile bullet spawn points.
Bullet Heaven: Bullets that shoot bullets appear (first?) in the boss battle of the 10th level. The developer's response to the page quote:
I even tried making bullets that shoot bullets that shoot bullets that shoot bullets that shoot bullets, but that turned into way too many bullets and went out of control.
Borderlands the best example are the MIRV mods for grenades, which are essentially cluster bombs. Anarchy-type submachineguns fire multiple bullets per bullet drawn from the magazine. Double Anarchy guns fire four bullets per bullet, albeit with poor accuracy. A rocket launcher called 'The Mongol' - It shoots rockets which shoot MORE ROCKETS.
Bouncing Betty grenades, which launch themselves to chest height and then fire a radial pattern of explosives. Honorable mention to the Rain grenades, which launch up to ceiling height and then rain explosives or fire/acid/lightning downward. Due to their large blast areas and high damage potential the Recursive Grenades are often the best grenades available.
S&S Orion: Aside from doing massive shock damage the bullets split into 3 smaller fragments upon hitting a wall.
In Borderlands 2, the Tediore Corporation's guns are simply gun-shaped explosives that somehow shoot bullets. Instead of reloading, you simply toss the gun at your target like a grenade, and a "new" one materializes in your hands. Rocket launchers are special in that, once you've fired all the rockets it can carry, the launcher itself turns into a rocket!
This is justified in game as they are real guns. Tediore is known for their quick reload speed and very cheaply made guns. The explosion isn't supposed to happen, so they market it as if it's supposed to do that.
There's always the Torgue-made MIRV legendary, and it's seraphic counterpart the Bonus Package and Meteor Swarm for when the entire room has to die, it's a standard grenade that spawns up to 12 (For the Meteor Shower, Bonus package maxes out at a slightly saner 10) more grenades, which each spawn another grenade when they explode. The main downfall of this abomination is that the player tends to get caught in the murderstorm as well.
Again by Torgue: In Tiny Tina's Assault on Dragon's Keep, SWORDSPLOSION!!!, a gun that shoots swords that blow up into three more swords. The Casual variants of Torgue's SWORDSPLOSION!!! gun shoot swords that explode into more swords that explode into MORE SWORDS.
Worms has clusterbombs and bananabombs. The latter is more fun. And the Sally Army. A wandering Salvation Army Action Bomb which explodes into exploding tambourines. Yes.
Jet Force Gemini features clusterbombs that detonate on contact and scatter in 3 smaller bombs. The smaller bombs also explode on contact, but to prevent them from exploding almost instantly, they deploy umbrellas to float gently to the ground.
Shotgun Ice in Mega Man X will break into chunks upon hitting something.
Similar thing happens with Freeze Cracker in Mega Man 7
Spread Drill in Mega Man & Bass splits up into two smaller drills up to two times when you press the fire button after launching it.
In Mega Man 8, the Arrow Shot upgrade splits into 5 bullets in a spread formation when it hits an enemy.
Into the Void, an obscure 4X, has missiles that fire lasers.
Descent has the smart missile, the earthshaker missile and the cyclone missile. The smart mine applies this trope to a stationary mine which releases Friendly Fireproof homing shots when triggered. From a gameplay physics perspective, some other Descent 3 weapons behave like this: the frag missile (which effectively releases Hyper Destructive Bouncing Balls), the napalm rocket, and strangely enough the impact mortar (its explosion is actually caused by a second weapon spawned when the mortar's timer expires). Since Descent 3 weapons don't spawn submunitions when they impact something other than terrain, it means you can use the impact mortar on an enemy point blank without blowing yourself up.
Ace Combat 6's final superweapon Chandelier is a giant cannon with shells that break up into dozens of cruise missiles near the target.
In an example that the player can use, regular cluster bombs, the Self-Forging Fragment Sub-munitions bomb(SFFS) and the Stand-Off Dispenser(SOD), all based onreal weapons.
Call of Duty 4: Modern Warfare There's a cheat that when you throw a grenade (including those you picked up), it will explode into five other grenades. And if you happen to pick up that grenade and throw it...
The bombs used in airstrikes for Modern Warfare appear to be clusterbombs based on the way the missile casings fall and the dispersion pattern as well.
To be more precise: White Glint with a VOB fires off a big missile. The big missile's case breaks open and reveals and releases several smaller missiles.
Team Fortress Classic has a grenade that explodes into even more grenades is part of the Heavy Weapons Guy's and Demoman's arsenals.
Team Fortress 2 limits this for balance's sake—the only instance that appears in the game is the Pumpkin Bomb MIRV spell from the Helltower Scream Fortress Halloween update. The spell fires a pumpkin bomb that travels like a grenade and explodes when it lands, forming a minefield of six smaller pumpkin bombs that have to be detonated by firing on them yourself. If the enemy sees the field, the pumpkins can be easily destroyed at range, like sticky bombs. This tends to make it more useful for faster, sneakier classes than any of the heavy hitters.
Sword of the Stars has the Multi-Warhead Missile. The sequel adds extra options such as an Honorverse-style bomb-pumped Heavy Combat Laser, a variant of the previous that fires multiple X-Ray Lasers instead, as well as a third that releases an Armour Piercing Heavy Driver shell.
In the Hunt has a green powerup gives your submarine these.
Custom Robo has a few guns which do this. One fires a missile which breaks into five homing missiles, and another fires a spike of energy upward that splits into more, pauses, then comes down. There's a few more along the same lines.
FreeSpace includes some bombs and missiles that'll spread either guided or unguided warheads when exploding - such as the Inferno or the Shivan Cluster Bomb. FreeSpace features Subspace Missiles too - but that's a bit different. You send a Tag'ing missile (or eventually paint the target with a laser) - which spawn plenty of missiles from subspace to crash on it.
Don't know about the first game, but the sequel has similar weapons filed under "Bomber Supression Missile[s]" — Awesome, but Impractical, as it's nearly impossible to hit any bombers with those. Suprisingly, however, they are very effective against enemy cruisers, which are too slow to escape the blasts, but low-armored enough for the missiles to do a lot of damage.
Gunman Chronicles has grenade launcher, which, after some upgrades, may fire laser tripmines releasing a number of explosive balls on activation.
Homeworld 2 brings us the Higaaran Torpedo Frigate, whose torpedoes travel towards a target at a certain distance before splitting into four small, but quick and agile missiles that chase down said target. The Recursive Ammo serves as as a deterrent against targets that are smaller than the Frigate itself. If the target is destroyed before all four hit, any missiles which are left will try to find another target to kill.
Gunbound has this with the Kalsiddon. Shots are fired normally until they split apart into two or four missiles and a homing beacon. The SuperShot compounds this by having the shot split into 4 missiles and a beacon, and then each of those missiles split into two with their own beacons. All 8 shots hitting will cause extreme damage.
FunOrb Arcanists have the Arcane Bomb, a grenade that releases three projectiles when it explodes.
The Rogue Squadron games have cluster missiles on certain ships, which split into multiple projectiles when fired. Not quite as useful as a single missile until you pick up the Homing upgrade, which then allows the missiles to wipe out entire squadrons of TIE Fighters in a single shot. Later games also give the Y-Wing's bombs a cluster effect, spreading the damage over a wider area.
Though not strictly ammunition, most of the Evil power enhancements in inFAMOUS do this. Most notably the grenades, which split apart when they launch, and the Megawatt hammer, which has six smaller balls of electricity trailing off of it.
Half-Life 2 has an Abnormal Ammo variant — big mortar shells delivering several headcrabs who do the whole target-hunting part.
Wing Commander Prophecy and its sequel Secret Ops has the Tracker missile, which consists of four Friend or Foe missiles mounted to a common frame, that break off after running a certain distance to allow the individual missiles to track on whatever target meets their targeting parameters.
The Ratchet & Clank series often has such weapons in their games, which include large bouncing mines that explode into smaller ones, or guns that launch deadly discs that split into more discs upon contact.
Crimsonland. The Splitter Gun's bullets split whenever they hit, causing mayhem on a screen. However, it's the only weapon that can kill you.
God Eater: The game allows you to take this to ridiculous levels with its bullet creation system. It is entirely possible to make bullets that shoot bombs that shoot more bullets that shoot lasers and lightning.
Star Trek: Shattered Universe, a space simulator game set in the Mirror Universe, has a Federation attack shuttle which fires torpedoes that split into six smaller torpedoes. One volley is usually enough to bring down another fighter. It is the most powerful player ship in the game.
Cluster torpedoes, which fire like normal torpedoes but split into a medium sized but extremely dense (normal mines deploy 4 in an area about as big as a ship this deploys 20+ in that same area) auto armed mine field (the mines the track in to the target).
The Bio-neural Warhead, a large tricobalt torpedo with point-defense turrets.
The Variable Auto-Targeting Armament, the unique console of the Starfleet Avenger-class battlecruiser. VATA fires a pair of missiles whose effect and submunition vary by which cruiser command is active on the Avenger. The shield booster command causes the VATA to shoot tachyon beams that damage shields, and do an Area of Effect shield debuff when they hit. The weapon efficiency command makes it shoot quantum torpedoes and hit for pure kinetic damage. The maneuvering booster command turns both into chroniton weapons, which do damage and debuff speed and maneuvering. The Klingon Mogh-class, stats-wise a clone of the Avenger, has a similar console.
Tribes: Ascend has the MIRV Launcher, a large handheld mortar which fires a small shell that explodes into multiple submunitions after about a second, covering a whole area in big blue explosions of doom.
In Escape Velocity Nova, the two most powerful Polaris capital ships mount a weapon known as the multi-torpedo. A decent salvo of these will reduce entire fleets to free hydrogen.
The X-Universe calls them swarm missiles. They run the gamut from worthless (Cyclone missile; although it fires a single warhead at first, it will split up into several of them if it misses its target) to dangerously effective (Tornado missile, Typhoon missile) all the way up to Game Breakingly powerful (Shadow missile).
Fallout 3 has the Experimental MIRV, which acts a lot like a shotgun that fires mini-nukes. It's considered Awesome, but Impractical mainly because mini-nukes are a rather rare ammo type and there really aren't any enemies in the game that you'd need to use that many mini-nukes on to begin with.
Fallout: New Vegas DLC the"Gun Runners Arsenal is a DLC that adds many new guns and Ammo types. To make up for the lack of mini-nukes available in the base game, the DLC includes four new fun flavors of these miniature atomic bombs that you can buy, and a great new nuke catapult named "Esther" to launch them from. One of these new mini nukes, the tiny tots variant, is a mini nuke that splits up and becomes several more nukes. At range, this ammo type functions like a normal cluster bomb, pepping a wide area with several mini-mini nukes to kill a bigger region of mooks. This ammo also makes the nuke catapult a viable close range weapon as the sub munitions can be detonated at relatively close range without being harmed, so you effectively have a nuclear shot gun. To top it off the Tiny tots nuke only costs the same as a normal mini-nuke, (assuming that people actually sold normal mini nukes).
StarTropics has the Four-star. A throwing star that goes forward and then splits into four stars that fire in all four directions.
Postal 2's "A Week in Paradise" mod does like the Call of Duty 4 cheat mentioned above: One of the new weapons is an extremely dangerous explosive called the "Jihad Grenade". Play in Enhanced mode, and it splits into five grenades shortly after being tossed.
Aurora lets you design missiles and add an optional payload to turn it into a MIRV missile or Mine. Said payload could also be an MIRV missile or mine, so you can get Missiles shooting Missiles shooting Mines that shoot Missiles.
In Infinite Space, MRV and Cluster Missiles can be seen to split apart shortly after launch. They allow you to hit an entire enemy fleet with each volley instead of just one ship. Best when combined with the Formation Foe skill.
Master of Orion 2 missiles can be upgraded with MRV warheads after additional research, though the only visible effect is increased damage, price and weight.
G-Police has the Star missile. Upon firing it it instantly separates into eight smaller rockets that then all but Hit Scan on the target. It's less of a rocket and more of a cannon, really.
Rage has Killburst ammo for the pistol. It's unclear exactly how they work, even with the reload animation that shows the magazine being inserted.
The Gullwing in P.N.03 splits into smaller energy balls on impact with a target.
The version of Dark Firaga used in Kingdom Hearts 3D launches a fireball that travels in a straight line until it nears a foe, at which point it splits into a multitude of homing fireballs that converge on the target.
The Ryu Dragon and Tatsu Blaze dream eaters also have attacks of this nature, both being capable of launching fireballs that split into over a dozen more and scatter destruction over a huge area.
In Bloons TD 5, the Bomb Tower's path 1 tier 3 upgrade shoots bombs each contain 8 more bombs.
Angry Birds: The Blue Bird splits into three on command.
The Naval Ops (AKA, Warship Gunner) games featured a few of these weapons, notably the cluster missile and splitting laser. They tended to be Awesome, but Impractical as they split too wide between individual projectiles and fired too slowly to really provide decent saturation attacks.
Monster Hunter: One of the ranged weapon classes (for a while the only ranged class) is the Bowgun, a hybrid gunpowder-crossbow that launches various forms of capsule-arrows containing anything from sticky bombs to shotgun shells to paintballs. Most of them exit their casings only after they've left the barrel.
Portal: A promotional video mentions that the turrets encountered in game "fire the WHOLE bullet, that's 65% more bullet per bullet". For the sake of comedy, some of the cartridges end up discharging on impact in the video and sending the bullet and cartridge in different directions, but this never happens in-game.
Sid Meier’s Alpha Centauri: When a unit is designed, most of the weapons which can be chosen for it are a laser of some kind, and all of them can be made into artillery.
Twisted Metal 4 had the Rain Missile, Rain 2 Missile, MIRV and Auto Lob. In typical TM 4 fashion, they all did about the same thing, and one of them (or two?) fired lasers.
Ricochet Rabbit had several trick bullets, one of which would stop in front of the bad guy, pop open, and pull out its own gun to shoot.
The Simpsons: In one episode, Nelson was drawing a robot with guns for arms fighting a plane made out of guns that shoots guns.
In the original Duck Dodgers in the 24˝th Century short, Marvin the Martian's "Ultimatum Responder" gun fires a bullet that fires another bullet right in Daffy Duck's face.
The first widely used example was probably the shrapnel shell, which used a timed fuse to trigger a small explosive charge within that would deploy its payload of musket balls. So it was basically a giant shotgun launched from a cannon and rigged to shoot the enemy from over their heads. It was invented by Henry Shrapnel, whose name became a word we use to this day.
FASCAM (Field Artillery SCAtterable Mines), AKA "instant minefield", similar to the Generals reference above.
The military once experimented with a bomb that opened up to reveal... a swarm of bats. Little kamikaze bats with little incendiary bombs strapped to them. The idea was to drop these over Japan — most Japanese buildings being mainly made of wood. By the morning bats roost on or near important buildings, then timed bombs go off. There was a little incident where the bats escaped and took refuge in buildings all across the military base where they were held, caused some hefty damage. The Atomic Bomb was more expensive, but it was finished first and didn't accidentally go off on a friendly base, so the batty project quickly fell into obscurity.
A modern example of the above is the Starstreak missile which launches three laser guided 'darts' to increase the chances of a hit.
The traditional cluster bomb, releasing dozens or hundreds of grenade-sized submunitions, has been the subject of a 2008 limitation treaty, mainly because the high percentage of submunitions that go dud on impact like to stay around to make life miserable for quite a while. Notably, the US, China, and Russia are not signatories, and careful Loophole Abuse—fully deliberate—reveals that modern "smart" submunitions are exempt as long as they meet a number of criteria: bigger than 4kg, no more than 10 to a container, and have two self-disabling/self-destruct devices in case it doesn't hit anything. This makes sense, since the main purpose is to make sure they don't hang around like an unplanned minefield after the war's over.
As a response to the above, even though not truly bound by it, the US Army has developed the world's largest shotgun shell under the Alternative Weapon Program. Fired from the MLRS rocket system it uses 800 tungsten rods to achieve much the same effect as a conventional cluster bomb but without the unplanned minefields. A similar bomb exists, though with a mix of steel and tungsten and it is intended to attack targets in cities such as fuel storage or chemical weapons without hurting anyone else.
The GT-1, a glide bomb that could be dropped 20 miles away from the target at 10,000 feet. The bomb would gently glide down, and once it was just above the water, it released a Mark 13 torpedo.
Similarly, the ASROC, an anti-submarine weapon consisting of a ship-fired missile that dropped a homing torpedo.