I remember seeing an article where this person used a cd jewel case to fabricate a magazine for an airsoft mg42 semi auto. Vacu-form mg42 and mg34 plastic shells are available. What semi auto airsoft gun could be stripped down and put inside these shells. I have seen a video of an airsoft mg42
here is one link
http://www.cushmanpaintball.com/Airsoftpage.html
and the video
YouTube - Electric custom airsoft mg42