Required in New Jersey if your upper is part of a semi-automatic rifle with a pistol grip and a detachable magazine. If your barrel is less than 16 inches in length, a muzzle device can be permanently attached to extend the length to 16 inches to meet NFA requirements.

I use a steel pin, staked into the muzzle device first and then an oxy-acetylene weld which enables me keep the weld clean and flush to the muzzle device - a requirement for many aftermarket blast shield devices that are growing in popularity. A standard weld that is raised above the surface of the muzzle device will prevent most blast shields from attaching.