We have covered plenty of cool 3D printed items in the past. If you have access to a decent printer, you could always choose from a variety of awesome models to print. The Gears Of War Lancer happens to be an assault rifle with a chainsaw bayonet. The assembled gun is 85cm long, looking quite impressive.
MyMiniFactory has this object up for grabs for $299. If you have access to a decent 3D printer, you could always attempt to print your own. More information is available here.