Re fake guns--here's a light-weight resin Ithaca 37 Michael Biehn's Corporal Hicks used for some scenes in "Aliens":
http://www.encom.demon.co.uk/hicksgun.htm
I'd love to know what became of the real one he used for close-ups. The pulse rifles were cool, but the last time I checked the gun store doesn't sell 10mm caseless explosive-tipped ammo.