This is the brake I am wanting to put on it.

http://www.circle10ak.com/

I thought I knew for sure that the barrel length on my AMD was 12.5 inches, but after double checking on google, I see a lot of people saying it's 12".  Still, I am pretty sure some folks got it wrong, but want to triple check.

Also, I don't know if this brake will fit.  So if you can tell, and inform me, that would be great.  Thank you.

Just measured.  It's a 12" barrel.  Boooooo.

You'd need a 2" extension and thread adapter. Those are 24mm RH.

Thank you.

The length of the brake/extension assembly must be no less than 4.25". The assembly must be pinned and welded plus welded to the sight base. BTW, the barrel is measured by inserting a rod into the barrel until it stops on the closed bolt face. The rod is marked at the end of the barrel, withdrawn and measured. Typically, the two-piece extension brake assembly turns out longer than it has to be because they always use a standard 2" barrel extension. Then, because most muzzle attachments have to be 'timed' to sit in the correct orientation, the installer will fail to adjust it until it is timed when tight. They will instead get it close and weld it. Since there is slop in the threads unless drawn down tight, this puts the brake/extension at a slight angle. Then, when its fired, typically the vibrations break the weld because the assembly is not screwed down tight. The best alternative is the Tapco one-piece unit that is machined to look like the original brake but has a longer 'tail' to make up the required length. But you still have to adjust it so its timed when tight before welding.

Thank you very much for all of the information.  I started to give up, but found this...

http://www.cncwarrior.com/ProductDetails.asp?ProductCode=25001

It is the correct threading and length.  I have been considering purchasing for the last few days.  Getting it welded on isn't a problem, as I have access to a shop where I weld.  

Would this be tight, without a slant?

I also considered this...

http://ak-builder.com/index.php?dispatch=products.view&product_id=30042

I just can't decide cause I do not know what the change will be, with the first.