Muzzle brakes are legal in United States, including California, New York, and New Jersey. However, there may be some restrictions on their use, so it’s always best to check with your local laws to be sure.
Muzzle brakes are devices that are attached to the end of a firearm barrel in order to redirect propellant gases sideways and/or downwards, which effectively reduces recoil and muzzle rise (the amount the firearm jumps up after being fired). This makes it easier for the shooter to keep the gun on target for faster follow-up shots. Muzzle brakes are also said to make shooting more comfortable and reduce stress on the shooter’s shoulder.