G&A Basics: How AR-15 Muzzle Brakes Work
August 29, 2013
Contrary to popular opinion, the way muzzle brakes work is less voodoo magic than it is rocket science.
It's true, so you can leave the incense at Auntie Mildred's cottage when you head to the range to mount and tune an AR-15 muzzle brake. All you need is a wrench and a basic understanding of how a brake works in order to get the best out of it.
How Muzzle Brakes Work
Like the rocket drawings you saw on 7-Eleven comic book racks back in the day, muzzle brakes — also known as compensators — harness exploding gunpowder gases and "ejecta" — particles, burning and otherwise — and redirect them in order to change the acceleration, or movement, of the rifle. Baffles inside the brake create an expansion chamber, and holes drilled into that expansion chamber bleed gas off at various angles to the axis of the barrel. These gases provide jet-like force immediately before, during and after the projectile actually exits the barrel, resulting in effective muzzle redirection.
A close look at the brake/barrel interface and the brake's internal guts reveal that as a bullet exits the rifled portion and crown — the last point the projectile touches as it heads downrange — it enters a slightly oversized tunnel through the brake. It must be oversized to allow the bullet free passage — if the bullet touches the inside of the brake with even the pressure of a whisker, it will be thrown off and become inaccurate.
Hot gases boil into the muzzle brake the instant the bullet's base exits the barrel, expanding violently and traveling at several times the speed of the projectile itself. Blowing forward around the sides of the bullet and following it, the gases hit baffle after baffle and jet hole after jet hole, expanding into the expansion chambers and being redirected out the sides of the brake.
Where and how those jet holes are placed in the muzzle brake has a tremendous effect on the influence of the brake in terms of recoil and muzzle movement (direction). If the holes are drilled at a 90-degree angle to the surface of the brake, the force the exiting gas applies is different than if the holes are drilled with a slight angle forward or rearward. If the holes are drilled in equal spacing all the way around the brake, applied force works only to reduce recoil, not direct or eliminate muzzle movement.
To reduce muzzle movement — typically termed "muzzle jump" — the holes must be drilled in the top and sides of the brake, but not the bottom; taking it a step further, the holes must favor one side or the other to counteract the effect of rifling spin direction on muzzle jump. Believe it or not, rifling direction does have a rather significant effect on directional recoil.
Using a crescent wrench, you can tune your brake's effectiveness by turning it a bit at a time until you find that sweet spot. Generally, most modern barrels use a right-hand rifling twist, so the top gas ports should be slightly to the right of perfect top center.
Why We Use Them
Very rudimentary brakes — such as the slanted cut seen on the muzzle of many AK-47s — have no baffles or even gas ports. Instead, they just give the exiting gases a general shove in a direction favorable to reducing recoil and muzzle jump. Have you ever wondered why the angled cut on those AK-47s isn't oriented straight up? It's because turning it just past center or just short of center — depending on the direction of the rifling twist — helps keep the AK from jumping straight up by counteracting the effect of the rifling twist.
The most sophisticated, aggressive muzzle brakes generally incorporate both expansion chambers and gas ports, and sometimes very large, rearward-angled gas ports into their design. Often there are two or three massive gas ports on each side, and several smaller gas holes on the top. They are extremely effective — and obscenely loud — and are favored for very hard-recoiling rifles, or to completely eliminate the affect of recoil on competition rifles such as AR-15s. And yes, they are often set at a slight angle to counteract the rifling.
Brakes that have gas ports but no baffles or expansion chambers are popular for bolt-action precision rifles and big game rifles. Generally much smaller in diameter and featuring gas holes 360-degrees around the brake, they are somewhat less effective, but much quieter than more sophisticated, aggressive brakes.
Muzzle Brakes vs. Flash Suppressors
Before choosing a muzzle device, it's important to consider the primary purpose of your AR-15. If the purpose is self-defense, you'd be better served with a flash suppressor than a brake.
What's the difference? Muzzle brakes tame recoil and muzzle jump but are tremendously loud and usually spit a pretty good fireball. Flash suppressors, however, tame the flash generated when unburned or burning gunpowder particles and gases contact oxygen, but have little affect on recoil.
Flash suppressors are also much quieter than muzzle brakes, making them far more suitable for personal protection use, especially indoors where loud guns cause significant hearing loss. If nighttime or low-light shooting is probable, a flash suppressor will protect your night vision, but the flash of a muzzle brake will momentarily destroy it. In some scenarios, that alone could mean the difference between living and dying.
On the other hand, if you are competing in 3-gun events with your AR-15, the recoil dampening qualities of a brake can enhance your speed, and a properly tuned brake will eliminate muzzle jump entirely, keeping your sight in the same place through recoil. Double-tapping a target can be done quickly with a good brake installed.
Predator hunters and varmint shooters can also benefit from a good muzzle brake because eliminating muzzle jump enables the shooter to spot his or her own impact through a riflescope.
There are some crossover muzzle devices. While they aren't as effective at dampening recoil as a proper muzzle brake, or as effective at killing muzzle flash as a proper flash suppressor, they're worth considering if you want a bit of both worlds. The one I have the most experience with is basically a modified A2 military-type flash suppressor with no gas cuts on the bottom portion of the device. As a result, escaping gases are directed upward, reducing muzzle jump in a small way, and at the same time, flash is partially reduced.
There are a lot of good muzzle devices. However, I can't come right out and tell you that "X" brake by "Y" manufacturer is the best. Brake effectiveness depends on many things: body type, height, stance, hold, ammunition type and so much more. The only right way to pick the perfect brake for you is through trial and error.
Personally, I'm a performance kind of shooter. On an AR-15, I like more aggressive muzzle brakes and suppressive flash suppressors. Flash suppressors are a topic for another time, but for now, here's a list of 10 popular muzzle brakes to tame the recoil on your AR-15.