A battery tray expander i created based on an earlier work by MandalloreNerfMods as a an in between step for another project.
This allows you to install a much larger lipo (+5cm battery tray) but it makes it impossible to screw on a barrel attachment as a downside.
For that reason I made a version which extends the barrel and provides a new nerf standard barrel attachment point. You can find it here: https://www.thingiverse.com/thing:3340661
For printing purposes there is a version in 2 parts in the files which will need much less supports. You can glue on the front piece afterwards