Nerf sells a model known as N-Strike. They call it a "micro blaster for sneak attacks." But it is twice as big as it needs to be. Picture 2 shows before + after. After removing the handle (4 phillips screws) you can then cut off the rest of the excess with a hacksaw. I have separated the pump plunger so it can be stashed after pumping up the air chamber. The 3rd pic shows everything you want to keep within the circle, and excess outside of it.
The dart is also twice as big as it needs to be. It can be cut with a knife or scissors.
In this configuration, the projectile actually goes further than in the original factory configuration. There seem to be 2 reasons for this: 1) the factories' excess barrel length actually slows down the projectile. 2) We've eliminated excess mass from the projectile.
This, the second step is a record of mistakes. I thought it would be possible to cut it down even further, making it about as big as a lipstick, and then fill it from a compressed air blower. Unfortunately, sawing off the pump also removes the check valve. Any air you put in leaks back out.
It should be noted that Nerf says not to modify blaster or darts. I wore eye and ear protection, and gloves while hooking up compressed air. Further, I only used about 10 psi. Any work with compressed air should be done with caution. For the record, I say DO NOT USE COMPRESSED AIR. I did so at my own risk, trusting my own judgement.
I discovered that pvc glue works nicely on nerfguns. My scrap parts glued very strongly to pvc. This knowledge suggests other projects. I was also able to glue the nerfgun back together in the configuration that works.