I have a 12ga. Mossberg Maverick. Our local NAPA dealer was selling 9 LED flashlights with a LED laser. I drilled a hole in the flashlight’s screw-off base then used a machine screw to attach it to the tapped hole in the Mossberg’s barrel retaining screw.
Screw the flashlight back on the base under the barrel and use (2) 8” black nylon wire ties, figure-8-ed, to secure the flashlight to the barrel.
Voila! $6.95 flashlight/laser sight combo. If you bump it the laser alignment shifts at bit, but it still hits within 2-4” at the 5 to 10 yard range for home defense.
Good enough for me. I won’t be trying to shoot the gun or knife out of the home invader’ hand. ;-)
The only thing that I would add, is to shoot it a few times to make sure everything holds together. It is sometimes very suprising how quickly accessories work themselves loose from firearms. For about $5 shipping included, you can get a set of “hillbilly wedding rings” direct from China that may also do the trick. http://www.dealextreme.com/details.dx/sku.5819
I can also highly recommend their UltraFire WF-502B Cree R2-WC 250-Lumen LED Flashlight. This is an incredibly bright and long lasting light when combined with a rechargeable 18650 Lithium Ion battery. But don't use the rechargeable CR123 batteries with it. They rattle around and are temperamental.