I have MANY D-Boys rifles. To make a mag work, slightly trim the release tab at the top. D-Boys rifles Hop up feed tubes don't push this part back far enough to let the BB's out of the magazine.
Trust me on this, I tried everything at first, and this is what works. Just use an xacto knife to trim a little off the pointed end of the catch, and try it till it works.
As you can tell, it won't take much. Just pushing the mags up makes them work, so it's a tiny change that's needed.
Notice the D-Boys SPR in this vid has no problem shooting from the Marui magazine that's in it:
http://www.youtube.com/watch?v=58vIxWIkx8o
This gun is a tank! Check out how the heft of it hits my left hand...