I am in the process of building an A2 clone and have been debating how to permanantly secure the compensator to be NJ legal.  The standard A2 flash hider is illegal in NJ, but a muzzle break/compensator is legal.  I found one that is very similar in appearance to the A2 flash hider.  I know the typical way to secure it would be to pin and weld, but i really would rather not do that.  I was thinking of using a two part epoxy that is rated for high heat, applied to the threads.  I talked to a local gun shop that sells a lot of AR's and AK's and they said this should be adaquate.  I'm sure i will get a lot of critisism for this, but any opinions and information would be helpful.

When it comes down to it, it's your ass on the line. It is incredibly unlikely that at any point during the life of the rifle anyone will want to verify how you secured the muzzle brake; however, if they do I am certain one could argue the epoxy is not permanent.

The ATF established the standards for "permanent" installation of muzzle attachments, and most states use those standards.

The approved methods are welding (as I recall it has to be a bead at least 1/3rd around), blind pinning, and using a true silver solder/braze that melts at at least 1100 degrees.
Epoxies are specifically NOT legal.
Also, a problem is that even higher temp epoxies will break down with use from the heat, vibration, and extreme stress of the muzzle blast of firing and it'll come loose sooner or later.

Bottom line is, as long as no official ever has reason to inspect the job you can probably get away with it, but it IS a violation of the law.

Pin and weld is the most commonly used method. The ATF considers it permanent for the purposes of barrel extension.

Drill a shallow dimple into the barrel after making sure the brake is on correctly. remove the brake and tap the hole with a supersmall like 4-40 tap.. get some small screws and screw it in.. then drop weld on top and then dremel weld flush.. it will look great and be more legit than epoxy..

There are many write ups on how to do this..

Heres an archive page with pictures still intact that I did back in January 2013..

http://www.ar15.com/archive/topic.html?b=3&f=118&t=600474

Easiest route is no muzzle device at all - plain crowned muzzle is your answer

sorry, gotta be welded or soldered.  I'd avoid the solder because it means heating your barrel to 1100 degrees. many people have had no problem with it, but thats awful hot for my tastes

ADCO does a great job if you're not comfortable doing it yourself

Move to a free state

Might want to think twice about using one that bears a string resemblance to an illegal muzzle device.  I remember a thread where a guy (also in NJ) was scrambling to fund proof that he had a brake, not a flash hider before local police destroyed his AR.  It's your rifle, but think about it.

As a fellow NJ'er who's looked into this, it's either weld or 1100 degree silver solder.  If you have a drill press, you can put in the initial hole on your muzzle device and indent in the threads on your barrel.  Bring your upper w/ muzzle brake attached to a local welder.  Should be about $20 or so to do.  There is a guy in West Paterson that does it.  Look on New Jersey gun forums, as this subject comes up a bit.