I have a X200B mounted on my M1 S90:
It works great, couldnt be happier. This set-up should work the same on an M4. Mine is mounted on the Insight magazine tube rail mount. The B&T mount is nicer, but the Insight munt works just fine. I am also using the new Surefire XT07 tape switch/tail cap assembly which also works great for this application. I prefer to have any weapon mounted light mounted directly in-line (vertically) with the barrel of the firearm (Shotgun, Carbine, Pistol) as it is more practical when clearing corners (left or right). The X200 is a great choice for a weapon mounted light for any shotgun as it is very light weight, it is bright enough (depending on your application), and since it is an LED, it will stand up to the recoil without issues. I believe the X200 is far superior to any other pistol mounted weaponlight design out there, especially the Insight lights. Hope this helps.
ETA: Here is a link for the B&T mag tube rail mounts. I would recommend the single rail mount #BT21458 $74.95 as it will allow you to mount the X200 in-line vertically with your barrel: B&T M4 magazine tube rail mount
Stay safe,
Nick
[ 11-29-2006, 04:44 AM: Message edited by: nickdrak ]