In most states it is not required to have a pinned and welded muzzle brake or flash hider. Only a few require such so as to prevent a firearm from having a threaded barrel. Usually that requirement is made so that you can’t easily attach a silencer to the firearm. Without much surprise you can get suppressors that work with muzzle brakes for quick detach features. Making this all really a silly thing in the big picture.
So besides those states why would you ever pin and weld a muzzle brake onto your gun? Unfortunately it’s all because of a minimum length requirement. Having a barrel less than 16 inches on a rifle turns its classification into a short barrel rifle. Which would need a $200 tax stamp from the ATF to legally own. To avoid the firearm being classified as a short barrel rifle, folks will pin and weld onto it a muzzle brake to bring its length back out to the 16 inch minimum.
But why make your barrel less than 16 inches to start with? Look at the detractors first:
- Less accuracy, a longer barrel will always reduce your cone of fire thus making it more accurate.
- Less velocity, most rifle cartridges are based around a 16 or 18 inch barrel. Being less than that means less powder is being burned and used.
- Barrel material, some barrels simply can’t be cut down due to what they are made of and how they were heat treated. It could potentially introduce cracking, flaking, or even damage to barrel linings.
- Uneven twist rates, cutting down a barrel or picking a shorter than normal barrel length for that twist rate can make the bullet unstable in its flight, creating wider shot groups or even keyholeing (the bullet hitting the target sideways).
- Disruption to natural barrel harmonics, resulting in opening up shot groups.
Usually customers don’t mind a little loss of accuracy or a bit less distance in the capabilities of their gun. But the last few mentioned is something critical to keep in mind. Some barrels are very specific in how they are tuned, in materials, twist rate, heat treatment, and barrel profile. Disrupting the design of the barrel by cutting it down can have major effects to it, including a possibility of baffle strikes inside of a suppressor if you attach one. So the real question comes down to what do you have to gain from cutting a barrel down?
The only reasons we get is that someone wants to mimic a certain style of firearm such as an M4, or want a little bit shorter gun to transition from inside a vehicle to outside but want to stay to minimal legal lengths. And there is no problem with that! But we always strongly encourage getting a barrel specifically made to such a length instead of cutting one down so that you can get the highest quality results out of it. Barrels made to be the often needed 14.5 inches will have an optimized twist rate, the harmonics shifted with changes to barrel contour profiles, through barrel coatings inside and out, and correct tempering and heat treatment of the barrel for that length. Several factors that will make it shoot circles around a barrel that has been cut down.
Long story short, it’s cool if you want an Mforgery (reproduction m4) but spend a bit of extra money and get a barrel that is made at the factory specifically to be used for that application.