What is "deadspace" in nerf?

 I've heard lots of people talk about deadspace when talking about new barrels and stuff. What does this mean?

Re-design7 years ago
It's the volume of empty space around the plunger.  This empty space does nothing to give you velocity infact it reduces velocity since it reduces the pressure on your projectile.

Eliminate the extra space and all of the pressure acts on the projectile.