A fairly simple amplifier device for airsoft guns with 14mm threaded barrels. It should print cleanly without a brim, raft or supports.
This will convert the sound of the airsoft shot from a puff or thud into a higher pitch snap or pop, much like the commercially available versions (madbull/socom gear KX3 and KFH amplifiers). Effects will be different based on how much air the airsoft gun is putting out, and where the barrel ends.
For reference, my test platform has a Woverine airsoft HPA engine inside, so air volume output is slightly higher than on an electric airsoft gun; my inner barrel also ends right at the crown of the outer barrel, which is very close to the optimal distance for this particular amplifier design (optimal is 1-2mm longer than the crown of the outer barrel).

The design is self-threading, add a drop of WD 40 or silicone lubricant on the threads of the outer barrel and screw the amplifier on. The first time will be a bit difficult, but after you remove it and blow the dust out of the newly cut threads it should go on easy. It is much easier to get the AMP to go on straight if you use a razor knife to cut a light bevel on the bottom edge where the 14mm hole is located. If you over-tighten the amp you will probably strip out the threads, so be careful. If you do strip the threads, a quick fix is a small amount of polymer clay, JB weld, or epoxy brushed onto the outer barrel threads (coat the barrel threads in grease and plug the barrel first).
Print at 1.01 scale to account for ABS shrinkage, printing at 1.00 scale should still work but it will make the first attachment slightly harder.
Make sure your printer is well calibrated, as the wall behind the indented lettering is fairly thin and can be prone to delamination failures or breaks in the wall on machines that aren't well calibrated.

See it in action here: https://youtu.be/VLO7v527Aqg