this is a conversion for an airsoft toy m4 hicap magazine (TM spec) either with the winding wheel or pull string flash magazine.
The box magazine will hold about 1,800 6mm bb's. you need to drill or cut 2 holes in the body of the original 300rd magazine. the holes need to be near the middle toward the rear of the magazine. there is also an opening in the bottom for the magazine to extend a little bit to access the winding wheel.
there is also another hole to fill the box magazine from the front. i included threading and a cap so it can be closed.
there is also an optional ammo belt 'door' if you want to use your own ammo belt for realism.
the print comes is 2 major body pieces which can be epoxied or welded together. supports will be needed for the top half. when attaching the box to the actual magazine, i used hot glue from the top and bottom.. you can use epoxy for a permanent bond.
PS: If you would like the files to the 3d printed airsoft toy in the picture, please email me at: alexdeguz @ hotmail dot com