This is your XQJ-37 plasma cannon. The only trouble is that since the old model XQJ was cobbled together from junked Amiga motherboards, you can only have one shot on the screen at a time.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 Golden Eye 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 examples are Older Than the NES, although 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. Made possible by the Painfully Slow Projectile. When applied to more permanent things, especially in Real Time Strategy games, it's an Arbitrary Head Count Limit. Contrast Bullet Hell, where hundreds, possibly thousands of bullets can be on screen at once.
— instruction sheet for Apeiron (a shareware Centipede clone by Ambrosia Software)