ive made a block render with .json when placed in world but I don't know how to have it render when on hand

I'm assuming you would need to create an item model for the block as well. Do this the same way you would use the model for an item in json, except use the block's name. You can see an example file in the forge source.

Here's what worked for me.

 

Put this just after you register your block:

ItemBlock myItem = new ItemBlock(myBlock);
GameRegistry.register(myItem.setRegistryName(myBlock.getRegistryName()));

 

Put this in init:

Minecraft.getMinecraft().getRenderItem().getItemModelMesher()
            .register(myItem, 0, new ModelResourceLocation(item.getRegistryName(), "inventory"));

I would recommend using

ModelLoader.setCustomModelResourceLocation

/

setCustomMeshDefinition

in preInit rather than

ItemModelMesher#register

in init.

 

Regardless of which method you use, this must only be done on the client; so do it from your client proxy.

 

You can see a more generic way to register a

Block

and its

ItemBlock

here. This makes use of several Java 8 features (functional interfaces, lambdas, method references), you'd need to replace these with the corresponding Java 6/7 features (Guava's functional interfaces, anonymous classes) if you're not targeting Java 8.