I couldn't find anything that does this so I made my own, based off of CJdoeshobbies's muzzle adaptor. I really like how it turned out.
Tested and works great with most attachments. Remember to always use barrel spacers for a tight fit and no wiggling.
The body should friction-fit well enough for casual usage (and will still be easily removable), but there's a screw hole in the bottom for affixing it more firmly.
Included is a version with two clips for holding shells. I like to use shells that you have to remove to reload, so the clips make reloading much more convenient. They're optimized for my shells (link above) but should hold any pilot-bore shells decently. If you don't want the clip then use noclip.stl instead of the other files.
Rival/Mega ammo will still fire as normal with this attached, but do note that most barrels won't work with them.
clip.stl | 59.3KB | |
muzzle.stl | 270.9KB | |
noclip.stl | 259.2KB |