The CB short has the powder space volume smaller than the CB Long.
Both the CB Long and CB short have ~ 0.45 gr powder.
So they both can stay below 1 atmoshpere of muzzle pressrue with a 24" barrel. So they have sub sonic gas escapement, and sound like a BB gun.
But the CB short will get more velocity and less accuracy.
[Higher expansion ratio, and longer jump to the lands.]
Recent batches of CCI CB short are much more accurate than a few years ago.