Unless this is a wall-hanger, please avoid MDF. At these sizes and weights, you may as well have made a real gravity hammer. I'm usually guns-ho about realistic props and such, but if your brother drops this, or mishandles this, it's gonna bludgeon someone in the head and give them a concussion. The length of the handle doesn't help either, it'll be almost impossible to hold and pose with. Not to mention you won't get much detail, most saw blades are gonna give you tear-out on all of the edges, which you shouldn't sand without a respirator.
And don't say I don't know what I'm talking about, I've handled, cut, sanded, and painted MDF. The one time I didn't wear PPE, the dust from sanding it gave me a horrid nose bleed and cough, and my nose was burning like I'd snorted a line of salt. This is not the project for that material. Use extruded insulation foam, it'll be much safer and lighter. Save the MDF for the rifle/pistol builds.