Allow me to plagiarize Bushmaster.coms tech-support site. The overall physics’ of this scenario should be identical, and i believe you should find it very helpful.
"...In our experience, the most accurate muzzle is the post-ban crowned muzzle. Many competition and target shooters we have talked with confirm this. As the bullet leaves the muzzle, you want - for greatest accuracy - to have no alteration of, or influence on, the bullet's flight. With an 11 degree
competition crown, the gases behind the bullet flow out in an even pattern of dispersal at the instant that bullet exits the barrel. This affords the least chance of disrupting that bullet path..."
"...We have tested our brake on post-ban and pre-pan barrels to see what, if any, effect they have on accuracy - it does not affect accuracy to a great degree. When you send a bullet out of the barrel and then through a muzzle brake, you are influencing it with gas pressures from various directions (depending on the type of brake). These gas pressures can alter the flight of the bullet - and therefore its destination accuracy. Granted, we're splitting hairs here as the time spent by the bullet in the muzzle brake can only be measured in nanoseconds, and the amount of force exerted by gas pressures would be difficult to measure at all. But, these gas pressures do exist, as the purpose of a brake is to alter the flow of the gases and to use the energy of that redirected gas flow to control muzzle rise. This becomes an important consideration to an L.E. Officer when that 2nd shot may be the one that saves his life - and, the amount of accuracy lost to the muzzle brake may well be inconsequential at the distances involved in a firefight with a bad guy. However, at the distances a tactical team sniper or a competition target shooter is concerned with, the loss of any amount of accuracy may be the difference between success or failure. It comes down to a question of choice based upon intended usage of the rifle.
An AK Brake will add 2.25" to your overall length - it has no effect on bullet velocity. We also make a 5.5" version of this brake for use on our 11.5" barrel - to reach a total legal length of 16". We also have some new brakes - called the Y Comp and the Mini Y Comp - that are very well designed...."