I just finished putting it all back together, i happened to have a tm m4 mechbox on the bench too so i popped the nozzle out and measured the up, it's 1/4" shorter than the scar.
http://picasaweb.google.com/RikyTic/20070404Scar I also decided to use something thin to place as shims on either side, but i used some of the thin covers you take out the back of your computer when you install a pci card, safer than getting a razor blade peice in the eye.