Everything has been said really about muzzle brake, but I can't help but add that IMO muzzle brakes are yet another device that have been added to the list of gadgets sportsmen use to allow them to shoot rifles they do not take the time to learn how to handle and shoot properly. Another quick fix adapted to small arms for hunters so they can shoot rifles and cartridges they probably should not be shooting.
Muzzle brakes have a purpose in allowing the military to make large caliber/long distance armament more portable and so that they can be handled and shot by personnel in the field without later having to pack them off to the field hospital for treatment. Over time they have found their way into the civilian market and adapted to small arms for hunters.
They are obnoxious and they cause damage to the hearing of other individuals around the shooter. I am sorry but the bottom line to me is that they are another ME device, where the shooters place their perceived shooting comfort over the possible negative consequences for everyone else around them. Barring medical problems, there is no excuse for using these things unless you insist on pushing the envelope on what a mortal man is capable of handling from the shoulder.
If you can't handle a .300 mag. in a properly fitting rifle without a brake on it then you probably should be shooting a .30-06 or a .270. If you are going brown bear hunting or after a cape buffalo and can't handle a .375 or a .416 without a muzzle brake then you probably have not spent enough time shooting that rifle, and are not familiar enough with it to be out chasing dangerous game with it in the first place.
It is not reasonable, nor logical, to expect everyone else in the bush that comes into contact with you to wear hearing protection so that you can use a muzzle brake for your own personal comfort because you can't be bothered to invest the time and effort into learning how to shoot a big bore properly in the first place. The use of muzzle brakes when hunting in a group, with a guide/PH, or in situations such as Calhoun described, shows a complete lack of consideration for others.............which is oh so common with the ME generation.