The DPMS ones suck. One of our local PD's got several DPMS M4's with the 4 position selectors. They sent them ALL back and replaced them with burst only. DPMS 4 position selectors go clockwise from safe to auto to semi to burst. The DPMS one is designed to work with the selector stops.
This is the DPMS set up.
[img]http://www.hunt101.com/img/079391.jpg[/img]
The Colt 4 position trigger is much better. It goes safe, semi, burst, auto. Colt removed the selector stops and uses a longer selector. It was very easy for me to move the selector to any position I wanted. What was fun was going from safe strait to auto by just flicking it up with my thumb. I have only seen them on the M4 Commando Enhanced models.
Here is a pic.
[img]http://www.hunt101.com/img/054136.jpg[/img]
If anyone is interested I believe that RRA makes a semi selector just like the one in the pick. I saw it for sale in the Brownells catalog