Guns in some games (space shooters especially) have a wildly fluctuating reload rate that suspiciously appears to be tied to the number of its bullets that are still on the screen. As soon as the bullet hits a wall or enemy (without ricocheting), or leaves the screen, another one is free to shoot.
How is such a thing possible? Perhaps you are armed only with the one bullet, which, much like a yo-yo, immediately returns upon leaving your line of sight.
More broadly, this is a general phenomenon where only a certain number of X are allowed to be present at one time; after that, you will either be prevented from creating new X, or the old X will start to vanish inexplicably. Typically this is done due to memory limitations. A good example of this is environment damage - you can only have so many bulletholes (for example, in GoldenEye (1997)). Another example is new enemies not spawning until you kill some existing enemies. Bullets are simply the most obvious example, since it's pretty evident to players when a shot they tried to fire doesn't fire.
(Note: There is a plausible case to be made for a remotely-guided weapon system only being able to control N projectiles at once, such as the real-world Phoenix air-to-air missile deployed on the F-111 and F-14; but the space shooter bullets aren't guided.)
Most famous examples of this trope are due to the technical limitations of old 8-bit hardware configurations. The Atari 2600's specialized hardware for rendering "missile" sprites could only handle two missiles at a time, leading to the two-bullet limit of many 2600 games. Interestingly, the oldest video game did not have this limit.
Outside of retraux games, it's subjectively discredited at this point; the replacement is a firing rate, which prevents this from becoming an issue beyond a limited scope. The upside to this trope is that it can encourage players to get closer to enemies to do more damage, creating a risk\reward balance, or to prevent a certain tactic from being used exclusively.
Contrast Bullet Hell, where hundreds, possibly thousands of bullets can be on screen at once.
- The Legend of Zelda had an upper limit to the amount of Sword Beams and arrows the player could unleash at a time.
- And the N64 games both allow only one magical arrow to be shot at a time (including the massive cooldown after each magic arrow.)
- In Cave Story the number depends on the weapon. The Blade is one of these weapons, with the added bonus that the number of shots on screen is the only restriction it has on fire rate. Because of this, at level 2 it deals insane amounts of damage at point-blank range, since its projectiles disappear right after hitting their target (the level 3 version keeps going, so you have to wait for it to vanish before firing it again.
- One of the many annoying gameplay mechanics in Deadly Towers was having to attack with slow-moving throwing swords, of which only one could normally be on screen at a time. The Double Shot allowed you to have two swords on screen, and so did the Parallel Shot except they had to be fired at the same time.
- Most Fighting Games, more often than not, allow a character only one projectile on the screen at once. There are exceptions aplenty, but for the most part, it's limited to one for the sake of game balance (to allow the other player ample opportunity to defend or counter).
- In Dissidia: Final Fantasy, The Emperor's primary means of HP-destroying offensenote is Flare, an extremely large Painfully Slow Projectile that makes up for it by strong homing and staying on the screen a very long time. There can only ever be two on the screen at once, presumably for reasons of game balance rather than technical limitations; if The Emperor could spam Flare, given its homing and duration, he could completely shut down the opponent with zero effort on the player's part.
- Team Fortress only allows eight pipebombs active at once. This limitation was added because some players tried filling the entire level with them to kill all hostiles at once; that and you'd probably hit the upper limit of ~600/768 entities in the original Quake engine. As such, this limit prevents spamming meant to kill off a full team in one swoop.
- Also true for the sequel. The Sticky Launcher can still only place 8 bombs. If you shoot any more, the first ones placed start detonating in sequence. The second launcher available, The Scottish Resistance, can have 14 bombs out at once, but will only detonate the ones you are actually aiming at when pulling the trigger. Other projectiles in the game (such as rockets, arrows, flares and syringes) are only limited by their firing and reload rates. This provides an interesting inversion where single shot weapons such as the Crusaders Crossbow fire as fast as they reload, meaning there was no point to giving it any fire rate. Cue bottomless magazine cheats...
- In the Half-Life series, only one laser-guided rocket can be launched at the same time; this is because reloading requires Gordon to point the launcher away from the center of the screen, which would thus prevent the player from actually guiding it with the laser.
- Space Invaders may be the Trope Maker. This makes comebacks possible, as you can shoot more rapidly as the Invaders get closer... provided you don't miss, that is. The Atari 2600 version had a trick to get double shots: Hold the RESET switch and turn on the game, then let it go. Cheat or glitch? Nobody may ever know.
- Space Invaders: Infinity Gene has the classic ship as an unlockable. While it still adheres to this trope, that one bullet is a One-Hit Kill on anything, including bosses.
- Gorf: Also applies to some enemy attacks. Unusually, you can fire again while one of your shots is still on screen, but your original shot disappears.
- Galaga only lets you shoot two bullets at a time.
- It lets the enemies shoot eight bullets combined at a time. There is a Good Bad Bug that exploits this fact by making the enemies fire shots that get "stuck" so eventually they cannot fire anymore shots at all.
- Galaxian only lets you shoot one.
- Satans Hollow only allows one, but a weapon upgrade gives an additional shot and a second upgrade shoots a double/single alternating shot.
- Asterax, a somewhat Asteroids-like old Apple Macintosh shareware game, makes this the explicit benefit of buying better guns, with 4-12 shots from each player allowed on screen.
- Asteroids had a maximum of 4. In the Atari 2600 port, your limit is only two.
- The Gradius series limits your ship you to two on-screen shots at a time, and the same goes for your Attack Drones. In Gradius V, however, this limit is extended to four shots.
- The NES Spin-Off Life Force only allows one bullet on screen at a time, but your ship will immediately fire a new bullet when the old one is gone as long as the fire button is held. This means that your fire rate is inversely proportional to your distance from the enemy, making it a viable boss tactic to get within six inches of them and maul them in three seconds with your inexplicable machine gun of doom.
- Berzerk does this too. You can fire rapidly as long as it's point blank. (Do it against a wall up close for THE single most irritating sound you will ever hear in life.)
- Crystal Quest allows up to five onscreen player shots and unlimited enemy shots.
What do you mean that isn't very fair? It's extremely fair. For them.
- The Airwolf Licensed Game on Amstrad CPC had this limitation, particularly grating when some targets required pixel-perfect aiming (and the gravity kept changing it).
- Alive and well in all its Fake Difficulty in the FunOrb game Star Cannon; in the second level, your bullets are the last priority for the game, after floating space debris and (sometimes undodgeable) enemy swarms. Your firepower is reduced to about 1/3 of normal...if you're lucky.
- Mega Man (Classic) can only have up to 3 bullets on screen at a time. Some special weapons in the sequels only allow one of its projectiles on the screen (e.g. Ice Wall). In the later games, you can even buy an upgrade to increase it to five shots on screen at a time.
- His brother Proto Man, in part of the tradeoff for the slide and charge shot in Mega Man 9 (and presumably this applies in 10 as well), can only fire two shots at a time, though having the Proto Coil or Proto Jet equipped allows you to shoot three.
- Mega Man Legends has this as a stat for guns called Energy which is the number of bullets on screen, while Rapid is how fast it can shoot said bullets.
- Mega Man Zero does similar - at the beginning, the player can only have three bullets from the Buster onscreen at once, but after killing enough enemies with it, this is upgraded to four. Somehow. Later games made four shots at once a facet of some other upgrade, like the buster-focused X Form in 2.
- Contra has an upper limit, with the spread gun allowing 10 bullets on the screen. If you don't have enough for all five bullets, you can either get a 3-shot or single shot (as exploited in a tool assisted speedrun). Likewise, the laser was actually several parts of a shot fired at once, and if you fired while the first shot was still on screen, it would disappear, meaning if you tried to spam it, you'd have a very short range weapon on your hands.
- Using the NES advantage controller with "turbo" turned on (which would spam the button for you), you would shoot four bullets at a time.
- Super Mario Bros. allows you to have two fireballs on the screen as Fire Mario. Later games such as Super Mario World and the New Super Mario Bros. series kept this. It also goes for Ice Mario's freeze balls.
- A sprite-limit example: Milon's Secret Castle has keys which appear as sprites. If too many sprites (such as enemies) as already on the screen, the key won't be drawn; you have to clear out some of the enemies, leave the screen, and come back for the key to appear.
- I Wanna Be the Guy gives you four at a time. There's a glitch that takes this away in certain areas.
- Secret Agent also uses this. In fact, one of the power-ups is an upgrade which allows you to have two bullets at the screen at once.
- In Captain Comic, the number of Blastola Cola 'bullets' you can have on the screen at once is limited to the number of cans you've picked up.
- The Minimum curse in Pharaoh Man's stage in Rockman 4 Minus Infinity forces this upon Mega Man.
- Stinkoman 20X6 includes a limit of three Ki Attacks at a time. However, even if there are that many still on screen, the punching action that you perform to do so still counts as an attack, and will damage enemies.
- The first Duke Nukem game (the 2D one) limited you to only one energy bolt onscreen at a time, upgradeable to four by way of powerups.
- In The Castles of Doctor Creep, the game is limited to one shot per Ray Gun onscreen at the same time. (As in, if one Ray Gun shoots, it cannot shoot again until the ray disappears from the screen, but another Ray Gun can still fire.) This fact is critical in solving some of the puzzles the game gives you.
- This happens to banana peels and the like in Mario Kart; the old ones disappear as new ones are placed.
- In Command & Conquer, as long as the engine pioneered by Command & Conquer: Tiberian Dawn was in use (although it was gradually expanded as the series progressed), units armed with railguns (which were first and only introduced in Tiberian Sun and of which the unmodified game featured a grand total of two - Ghost Stalker and the Mammoth Mk.II mech) could have a maximum of one active railgun "line", even if the shot had already dealt all its damage. A railgun could not be fired again until the particle system of the last beam had entirely faded out, and in fact if one was to mod a railgun with a lower firing delay than the fade-out timer of the particle system into Tiberian Sun, the railgun would "jam" permanently after firing once and could never be fired again, even if the particle system had faded. Railguns didn't appear in the series again until after the switch to the SAGE engine, in Command & Conquer 3: Tiberium Wars, but the code remained and they can be re-created in Command & Conquer: Red Alert 2 and its expansion through modifications of the game files. It is uncertain why this limitation exists, but as it never becomes apparent in the unmodified game and is mostly a footnote to creating modifications that contain railgun weapons, it is most likely an engine limitation, rather than a conscious nerf in the interest of game balance.
- In the Mega Man Battle Network series, you can only have one buster shot out at a time (they're invisible, but do have a small travel time), meaning you can shoot a lot faster at point blank range.
- All Shoot'em ups only allow one super-attack (smart bomb, nuke, etc.) at a time, either waiting until it finishes or after a fixed delay; in two player games, there might only be one on-screen bomb among the two players. Spamming bombs tends to be counter-productive depending on how the game works, either because the bomb blocks bullets, a short invulnerability is conferred, etc.
- It's also present in many of Action 52's games. Some of them still avert it, allowing to spray numerous bullets, but this often causes the enemies or bosses to not spawn.
- Hero Klungo Sssavesss Teh Universsse in Banjo-Kazooie: Nuts & Bolts.
- In Diablo, the sprite limit could be reached very easily with one Chain Lightning spell with many enemies in range or multiple Fire Wall spells. Sure, it's not a gun, but you still won't be able to cast any more until the effects finish up.
- In Diablo II, you can cast as many missiles as you like ... but then you might not see them. Hilarity Ensues when fighting against a multi-shot lightning-enchanted boss while you have slow missiles active, where moving in the wrong direction (or not at all) will get you kill by hot air.
- Glider PRO only allows two rubber bands to be on screen at once.
- Some games allow you to raise the bar with an in-game powerup:
- Jewel Master for example allowed you to raise different aspects of your spells (such as how many projectiles could be on-screen at once) by varying the levels of the rings that created them.
- La-Mulana has a ring that gives an additional projectile on the screen.
- In Metroid Prime, you can only have 3 missiles active at once. Normally their fire rate is so slow that this is completely irrelevant, but a an unintentional method of shooting them very quickly allows the limit to be reached.
- In Metroid Fusion, you can only have three beam attacks, two missiles, and three bombs active on screen at once. The beam limit usually can't be noticed unless you are falling and firing down, so it rarely interferes with gameplay. The missile limit is also hardly noticeable in that, early on, you won't have many missiles, so you'll be firing each one carefully, rather than firing them rapidly and potentially wasting them. By the time you have more missiles to work with, your upgrades will have reduced the rate of fire of your missiles, making the limit much less noticeable.
- Metroid II: Return of Samus had a limit of three beams, one missile, and three bombs on the screen at once. The beam limit is most noticeable when firing the Spazer or Plasma beams, since those actually consist of three beams fired at once (the Spazer fires them in a spread pattern, while the Plasma beam fires them in one line). If part of the Spazer hits an enemy but another part does not, often two of the beams will be out of sync with the third.
- In Wizard of Wor, a player may only have one active shot on screen at a time. This makes long shots across the maze very dangerous.
- Genetos gives you two bullets at a time with the first ship (taken almost directly from Space Invaders), and five with the second (modeled after ships in late-eighties games), then abandons the trope as you move closer to the modern day.
- MDK has it with sniper bullets... because each one has a camera attached, and you only have three displays.
- The various "Sub Hunt" style games (the first of which seems to be Depthcharge in 1977) where you control a ship and fight against enemy submarines by dropping depth charges on them. You have an unlimited number of depth charges, but a counter on the screen governs how many you can have in the water at a time. When a depth charge hits an enemy or the ocean floor, it "regenerates" back on your ship and you can fire another one. Basically the gameplay revolves around this mechanic as you must use depth charges judiciously or you may find yourself momentarily defenseless against a swarm of subs.
- It's not obvious unless you slow the framerate right down, but ranged weapons in Dwarf Fortress had this limitation imposed from V0.31 onwards; a second shot cannot be fired until after the game rolls to determine whether or not the first has hit its target. In older versions it was possible to fire so fast that six or seven arrows or crossbow bolts would be in the air before the first hit, which, combined with the fact that arrows or crossbow bolts had a high probability of a One-Hit Kill, means the rest of the shots were just wasted. (It did look badass though.)
- In Battlezone II: Combat Commander, the TAG missile fires a homing dart, which has a particularly bizarre bullet code. Under normal use, it will only fire one dart at a time, and will let you fire again once the dart flies past its 100 meter range. But if you fire off into the sky and hold down the trigger, you'll suddenly spray out a dozen darts if you aim downward once the airborne dart expires.