I have a Colt M4 6400c. How does the stock brake come off,and are there threads underneath it
to screw on a Flash Hider. or do I have to thread myself ?    

Some of the colts will throw the brake down range. Depending on your skill you can remove it your self. Get to  much of a freelancer witht the dremel and you will ruin the barrel. Is the 40 buks a smith would charge really that much when you will have to replace the barrel cause you cut halfway into it with your die grinder?

Is there really a Big differance in removing the Muzzle Brake ? will the Flash Hider shoot any differant ?
Should I go to all the trouble of taking it off... I shoot with iron sights and a TAO1 ACOG, it shoots real good right now !

Quoted: Less flash, less blast, able to add more cool toys like suppressors.

Yeap,I agree.The recoil check that was on my Armalite was a huge complaint getter at the range.Got some nasty looks from folks beside me over the years.The blast and noise to me was not something I cared for either.Like some have said in the past its a noise multiplier.And the more use it got the more it eroded and the louder it got on me.Blast was directed more to the rear as the ports rounded.It must have been made from soft steel causing it to erode the way it did.
Removing it was the best thing I have done to improve the Armalites performance and looks.I can now use it for high power also.
I installed a Bushmaster A2 FS,but Im wanting a Phantom.

cool, Thanks Guy's....

I'm waiting on a new barrel from rbprecision for my bushmaster M4 with that mini Y brake.

i am NOT going to shoot it again until I have a new barrel with a regular flash hider on it. That brake is horrible and wears on me fast at the range.