Brithunter
A still air chamber would have to be several feet long and of very large diameter to be affective in stabilizing a bullet, very long because a bullet does not stabilize in a few inches let alone yards, large diameter because the propellant gases move faster then the projectile and would be causing havoc within a small diameter tube. Of more importance in stabilizing a bullet would be a properly cut crown and the correct twist rate for the bullet weight, as well as bullet geometry.
A muzzle breaks use is to reduce recoil which with most shooters will result in less flinching and better grouping, If the firearm shot poorly because of an ill cut crown or improper twist rate before the muzzle break was installed it would shoot poorly afterwords but with less recoil.
I have built and sold many Sound Moderators both Silencers, and suppressors and have found no evidence that they stabilize a bullet, but they do reduce recoil.
As I said earlier, with the recoil reduced the shooter will practice more and their for his groups should shrink so a muzzle break does have a secondary effect on accuracy.