Hi-capa to M4 slim adapter

I use a Anet A8 the tolerances might be off for your printers to keep the mags in I use electrical tape and just friction fit it on
you could use a piece of plastic and tape to put in the hole which does line up with the mag release hole.

to make the bbs feed I just used a pen tube through the hole and super glued it in. You also have to modify the mags base plate to get the bbs to go though. and you have to super glue the whole thing together and to the mag.