Nice and working silencer for your airsoft gun!
You can use some foam or print Surpressor baffles: https://www.printables.com/model/366130-stackable-airsoft-suppressor-baffle
You need to scale the baffles to 104,38%/33,4 mm

Dimensions:
Lenght: 131 mm
Width: 40 mm

Made 3 files
1: 14 mm ccw
2: 14 mm cw
3: The top lid for the silencer

Print settings:
Recommend 0,2 layer height and maximum 0,24 layer height
I used 0,6 mm nozzle, 2 walls and 15% infill.