Here is something that came from my years of trying to make the quietest springer blasters. It is a 16mm (Caliburn) direct mount suppressor with integrated rifling for short darts. It works best with a TPU piston and TPU extended spring guide (Caliburn3 backbutt, C4 4BackB) to dampen spring noise. With the C4's airbrake, TPU piston and spring guide, and this suppressor, you can get a nearly silent C4.
This suppressor uses 2 concentric rings with small holes to bleed air from behind the dart into the outside chamber, where it is slowly released out of the front cap holes. The holes on the inner scar barrel are between the rifling.
This can only mount to a 16mm barrel.
It also works great with the Sillybutts SLAB with an extended barrel.
The author hasn't provided the model origin yet.