MP5k backplate for m4 style collapsible aeg stock, there's also shorter lr300 version without wire hole. I don't have a buffer tube to test it on, so please, if you make m4 version share your experience.

Print upright with supports, you may need enlarge holes just a bit to make it fit your gun.

[EDIT23.3.2020] Made new version https://www.thingiverse.com/thing:4236162 it will at least fit JG body.

[EDIT 17.3.2020] I have been noted that this doesn't fit some MP5k's, at least CA and JG(I have no idea about galaxy) have problems. I will post new versions soon.