I call it the gundam heaviest arm. This was made for the supernova kit. The rockets or railguns will not work with bandai's version. The foot track + cannon may though. Keep in mind this will need sanding, painting, and gluing as nothing is perfect, however, I tried to make it fit as snug as possible so it depend on your printer too. I recommend to print in ABS and then vapor bath. Check out my other works for the EW series. Check out my page for more customs.
There is also a group on facebook just for 3d printing for gunpla. I recommend you to join if you are interested. It's called 3d Printed Gunpla.
If you like what you see, and would like to support me, please donate to my patreon. This will help further my creativity and create more customs quickly.