Zinventor

The air restrictors function by limiting how much air can go from the piston to the dart. Once the dart moves the first 1/2 inch or so, the restrictor closes blocking the rest of the air in the piston. By doing that it limits the speed of the dart. When it is removed, all of the air in the piston can be used to propel the dart down the barrel. For some blasters, it does not make a large difference, but for others, it can make a huge difference and seriously improve the performance.

it is not the amplitude (volume level) that is the problem, but the basic nature of audio signals. Pins on a microcontroller are designed to work between 0 and 5 volts. the audio signal you are seeing at 250 on the ADC means that the pin is being exposed to -1.25 to 1.25 or greater when there are spikes like drum beats and such. the pins on a microcontroller are NOT designed to EVER see negative voltages, and it can cause irreparable damage to the chip. a headphone jack is more than capable of providing enough power to blow a pin, I've done it accidentally more than once.