My buddy makes his own comps....
Let me go see if I can find a video or two of his....hold on a sec...
A'yup, here it is:
http://www.youtube.com/watch?v=GzDKrpiayvMIt makes me laugh.

He has a bridgeport and a lathe.
He has built 3 USPSA Open division guns now.
If I recall correctly, the hole he drills for the 9mm Major compensators is actually 3/8ths...or 0.375.... with the bullet diameter being somewhere, I think, around .355.
So I am thinking that the barrel bushing drop in compensators have an I.D. that has to be bigger than the O.D. of the barrel...so the clearances aren't so tight as to effectively deflect the gas up through its baffles.
That, and the fact that the bushing slides back and forth over the barrel versus a traditional comp being screwed to the end of the barrel.
My buddy tinkers around making comps out of stainless steel and aluminum. The nice thing about aluminum is that it is light. The bad thing about aluminum is that the pressure from the high pressure 9mmMajor rounds erodes the baffles.
Stainless steel doesn't erode as quickly, but it is heavy. Heavy enough that my buddy can tell the difference.
He has tried working with titanium before but it was either the wrong alloy or he don't have the correct combination of tooling and skills to be able to tap the very fine threads that are required for a comp.
You really do have to reload your own ammo with a comp. You want a slow burning bulky powder because that turns into more gas which in turn works the comp even more.