This project was designed to replace the hop-up chamber of an AGM MP40 AEG.
It's meant to replace the genuine part, not to fit onto standard AEG barrels or other. So, you'll need to have the rubber parts present onto the barrel for it to work.
The first one is close to the genuine part.
The second was retouched for 3d printing, with a bit more space for the BB's and the nozzle to move inside it.
100 [%] infill, with supports everywhere (forgot to enable the support roof).