I have a bushy m4gery with the mini y comp...but on a 14.5" bbl it is really loud. Would it be legal to purchase a 14.5" bbl with 1/2"x28 threads and attach a levang comp to it if the OA length were 16"? What has to be done to make this attachment "permanent"?[peep]

The Levang is not post-ban legal.  However if you get one of the other approved post-ban brake designs (and you'd need one that would bring the 14.5" barrel out to a legal minimum 16" overall length - which most standard offerings won't do...).

If you got something like Kurt's extended A3 tac-brake, you could permanently install that on the 14.5" barrel to bring it out to legal length.

The conversion would involved grinding or cutting off the bayonet lug, and attaching the brake by one of these approved permanent attachment methods:
1) blind pin the brake with a hardened pin, and weld over the pin.
2) high-temp (1100F) silver solder
3) weld the brake over at least half its circumference

Thanks Circuits...but where do I get a look at such product...and how do  I contact Kurt?

Both Kurt Wala and Gunsmoke Enterprises offer the long post-ban compliant muzzle brakes.  They both have forums over in the industry forums section.

I believe both manufacturers have links to their websites, where you can see pics of their respective offerings.