I'm currently designing an air rifle and am looking for ways to increase projectile velocity without resorting to combustion, modifying the projectile, barrel length or changing max pressure within the container.
I've considered using a De Laval nozzle to increase the gas's velocity, but from what I've researched it would actually perform worse due to the decreased pressure on the projectile.
Thus, I've been looking for some sort of nozzle or other device with no moving parts to aid in increasing the gas's pressure, but haven't found any (poor wording when searching or does it not exist?). Is there such a thing?
Looking forward for answers.