Base plate for a Hi-Capa magazine ( gun : Hi-Capa 5.1 Marui ), there are two models , one for a PUNISHER base plate and one for a BIOHAZARD base plate:

The biohazard model is maybe to small, but thats normal, I made it so , so it can easily fit in the base plate , and can be easily glued to it.
For the punisher you will maybe need a dremel to finish the piece to make it fit smoothly on the base.

Made it for a request of a Friend who just thought it would be too expensive to buy, and it does´nt exist for his gun, so.. :)

Print Advice : For the Base plate, print them like on the picture, with the entrance of the rail at the ground

PS : For the Solidworks files, just say it, I have them.