How many lumens do you want, how do you plan to attach it to the firearm, and what's your budget? Is this for home defense, and if so what max range are you thinking about?
Most dedicated weapon lights are geared more towards spill than throw, so that may be somewhat of a challenge if it really is necessary.
You're definitely going down the right path in looking for a tough light with a single mode.
My primary 12 gauge has a Surefire 6P with their XM dual switch tailcap mounted at about 10:30 with the button sitting right by the front end of the forearm (semi-auto). It's got a Malkoff M61 in it.
When it arrives, I plan to install a Malkoff MD3 with M61HO in it's place. This should give the length I need to get the lens reasonably close to the muzzle while still giving easy access to the larger button of a standard Surefire clicky tailcap.
The title of the thread references shotgun/rifle. Do you plan to move this one light between different weapons?
Grizz