I really share your idea about wheathering.
I created some really rusty obis,for me and frends,visible by clicking on my signature.
I only can agree with your idea!
I think the original grenade form movie was probably a deadstock piece,which had only air patina,so you rust is not toob bad for such a result,however the brass part will need more weathering.
On original grenades,only the front near emitter was "new" because of a removable sealing part,other parts were in contact with air,giving dark weathered color.
It's easy to see when you have a complete grenade inthe hand.
First,they remove a little pin.
Then,they screw off partially the windvane to let it turn free(the little round shape on the neck is for maintaining the security ring).
Then,the grenade is shot,and we know the results....
When unused and air-stored(I mean,not dug item)the brass ring protects the brass under it,so its's the reason why the brass has "gold" color there,they just removed the cylinder.
If you want a better look on brass parts you would also weather the windvane inside.
Please use some ammonia,air process,suspend the piece over ammonia,and protect the front before,to leave it new.
If you want to create some weathering on aluminum,you can do it,just out in the garden,it makes rust,a little bit like steel.
) Finally, I rolled the grenade on a rough concrete slab, using by foot to REALLY damage it. Aside from a final rub-down with a clean rag to remove the concrete dust, that's pretty much it!
