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Home > Recoil 101
 

Recoil 101

"What Causes Recoil?"
One of the most common questions we get asked is "how do muzzlebrakes actually work?". There is a lot of erroneous information about that topic if you peruse the various gun-oriented websites, so we're going to provide you with a simple and concise explanation. Muzzlebrakes operate by some very simple physics principles that we're all familiar with. We are going to explain this in a step-by-step format and with a minimum amount of headache (hopefully). Most of us learned Newton's Laws of Motion at some point in time in our studies, we are going to look at each one, in order, because each is relevant to this topic.

Newton's First Law states:

Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

Basically this means that the gun is not going to move or counter recoil by itself. The gun will not move or exert force until a force is exerted on it.

Newton's Second Law states:

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

This means that how fast an object (bullet, gun, '87 Toyota, etc) accelerates is going to depend directly on the amount of force applied to it and the weight of the object. If you were to double the mass of an object, it would take twice as much force to keep the acceleration rate the same. From this Law we get the familiar equation:

F=ma

where 'F' is the force applied, 'm' is the mass of the object, and 'a' is the acceleration rate.

If you take this F=ma equation you can figure out how much force is generated from an object of a known weight accelerating at a known rate. Acceleration (a) is basically a change in velocity (v) over a change in time (t). The F=ma equation will give you the amount of force being applied during the acceleration. After the object stops accelerating you can calculate the amount of kinetic energy imparted to it through acceleration by the equation KE=mv^2 since (a) in the previous equation would go to zero. The KE equation is going to determine how powerful the bullet is, the F=ma equation will determine how much recoil it is going to generate getting up to speed. Remember this snippet, we will discuss it in the next
section.

Newton's Third Law states:

To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

This law is more commonly paraphrased "For every action there is an opposite and equal reaction". So if we accelerate a bullet forward, then the gun has to accelerate rearward. When you pull the trigger and the propellant ignites, it expands and pushes the bullet forward while at the same time pushing the gun back.  Therefore, the force of the bullet's acceleration is going to be equal to the force of the gun's acceleration (recoil). Lets put this in an equation format:

F=ma ----->ma [rifle]=ma [bullet]

so

F [rifle]-F[bullet]=0

Basically the gun and the bullet are going to have the same force exerted on them but the bullet will accelerate to a higher speed because it is lighter. If the bullet gets heavier/faster or the gun gets lighter, then the gun will accelerate more (kick harder).

Lets put some simple numbers into these equations to illustrate. If we have a rifle that weighs 7 pounds and there are 7000 grains in a pound then the rifle weighs 49,000 grains. For simplicity sake lets say that the rifle is a .308 shooting a 150gr bullet. Rather than get into the exponents and acceleration constants, we'll give the bullet a generic acceleration value of 100 since we're not specifying units of measurement, just figuring relative values.

Therefore, if we put this information into the ma[rifle]=ma[bullet] equation from last section we get the following:

49,000(a)=15000
a[rifle]=0.306 or 0.306% of the acceleration of the bullet (0.306/100)

It is now obvious how our previous statement about changing the weight/acceleration of the bullet or the weight is going to change the acceleration (recoil) of the gun. But wait, there is more forces involved in recoil than just the bullet acceleration. Although the propellant is burning it is retaining most of its mass, it is only changing from a solid to a gas. There is also a secondary acceleration of the propellant once the bullet leaves the muzzle. Once the bullet is out of the way, the propellant will suddenly accelerate a lot faster forward, creating more recoil force rearward. Since the forward acceleration forces are going to be equal to the rearward acceleration forces, we can reasonably calculate how much these additional factors are going to change the recoil. We will make a very conservative estimation that the propellant is going to make a 25% acceleration rate increase once the bullet leaves the barrel but only for 1/4 of the previous time, therefore we will list that force separately in the equation to keep things simplified. First we have to account for the forces.

ma[rifle]=ma[bullet]+ma[propellant]+.25m(1.25)a[propellant 2nd]

We're going to figure on a 150gr bullet again and 50gr of propellant.

49,000a=15,000+5000+1562.5
49,000a=21,562.5
a[rifle]=0.440 or 0.44% of the acceleration of the bullet (0.440/100)

In this scenario there is a 43.8% increase in rearward acceleration (recoil) over what would be created by just accelerating the bullet. 

Now that we've covered the basics in Recoil 101, lets go further and look into how muzzlebrakes reduce (not eliminate) recoil.

An efficient muzzlebrake will have an arrangement of ports and baffles to stop the forward movement of propellant gases and divert them at a perpendicular or rearward vector away from the direction the bullet is travelling. Stopping the gases creates deceleration forces that counteract the initial forces generated by accelerating the propellant mass.

Although there are some other small variables and such, we're going to go back to our previous equation and start factoring in the muzzlebrake changes.

ma[rifle]=ma[bullet]+ma[prop]+.25m(1.25)a[prop 2nd]

If the muzzlebrake baffles can completely stop 75% of the propellant then we will counter approximately 75% of the primary force incurred accelerating the propellant, so our new equation will be close to this:

ma[rifle]=ma[bullet]+ma[prop]+.25 m(1.25)a[prop 2nd]-.75 ma[prop]

If the ports can divert that same 75% laterally away from the bore, then the equation will now be something close to this:

ma[rifle]=ma[bullet]+ma[prop]+.25 m(1.25)a[prop 2nd]-.75 ma [prop]-.1875 m(1.25)a[prop 2nd]

If we punch our previous values in for the 49,000gr rifle, 150gr bullet, and 50gr propellant charge, we get the following:

49,000a=15000+5000+1562.5-3750-1171.9
49,000a=16640.6
a=.340

When we take that figure and compare it to our original 'bullet only' total, we see only 11% more recoil acceleration than this impossible scenario. If you compare that same figure with the real world total for the same rifle, the 75% efficiency muzzlebrake offers a recoil force reduction of 29.4%. By redirecting the propellant gases, the hypothetical muzzlebrake offered almost a 30% cut in recoil. Now we can also note at this time that a more precisely made muzzlebrake will let less gases out the muzzle. This would be more efficient and would give a greater degree of recoil reduction. Likewise, a less efficient muzzlebrake would give a lesser degree of recoil reduction since more of the propellant mass would continue moving forward. A muzzlebrake has a few ten-thousandths of a second to do its job, obviously efficiency makes a big difference with such a small amount of time available. Therefore, an efficient muzzlebrake should have a lot of baffle surface and venting cross-section to achieve good efficiency. In this first KA-1830 cross-section illustration you can see the propellant paths as the bullet is passing through the muzzlebrake (propellant flow shown in blue)

 

As the bullet passes through the brake, the propellant will hit baffles and vent outward.  The more propellant that can be slowed and vented during that time will determine how much recoil reduction is provided. When the propellant stops against the baffles, the pressure is going to force it to accelerate away from the bore of the barrel/brake. This causes the brake to accelerate in the direction opposite from the path of the propellant. Basically, if the port directs propellant out the right side of the brake, it will push the brake to the left. Therefore, it is important to counteract that force by arranging the ports so that they are equal in size, position, and on exact opposite sides of the brake. This ensures that the forces will counteract each other and not cause the brake and muzzle of the gun to move. On most King Armory brakes we run a '6/45' porting arrangement where there are 6 rows of ports seperated by 45 degrees and each row is 180 degrees opposed to another row. This end view illustration shows this layout clearly.

Notice how each propellant stream pushes directly against another, this creates a neutral braking effect as opposed to a compensator which is used primarily to redirect propellant upward to help hold the muzzle down under recoil. KA's '6/45' arrangement allows a large amount of venting and baffle surface while keeping the top and bottom of the brake enclosed so that blast is not directed into the line of sight of into the ground where it will stir up excess dust. Our KA-1830 brake uses ports of different sizes, but they are each positioned opposite a port of the same size so there is no movement of the muzzle. This reduces its impact on barrel harmonics and accuracy so your rifle doesn't lose anything by adding a muzzlebrake.

Another muzzlebrake design that is effective for recoil reduction is an angle-ported arrangement which redirects the propellant gas rearward to actually generate a forward force on the rifle. By this arrangement it is possible to actually reduce recoil more than is possible with a standard baffle-type brake. However, these type of brakes work best with larger cartridges that generate a lot of propellant gas and recoil so you will usually see this type of brake on larger rifles such as the 50BMG or .338 Lapua. The same basic equation ma[rifle]=ma[bullet]+ma[propellant] applies here, but in addition to recovering the force of accelerating the propellant, the angle-port brake will generate additional recoil reduction by redirecting the propellant. This creates a 'reverse recoil' effect, by accelerating the propellant rearward, the brake and barrel are pushed forward, further countering the recoil of accelerating the bullet. Optimally, an angleport brake will approach ma[rifle]=ma[bullet]-2ma[prop 2nd] wherein the recoil of the gun would be less than that generated by only accelerating the bullet. Angle-port brakes have a few disadvantages that make them less optimal for some applications though. Due to the required baffles and ports they are larger than a standard brake and usually heavier. Also, due to the blast being directed rearward, it increases the noise level at the shooter's position substantially. This type of brake is used when the need for recoil reduction outweighs weight and noise concerns. These are a good choice for rifles that are very light for their power level or for applications where additional reduction needs to be drawn from a particular cartridge to make the recoil manageable. King Armory has a few angle-port brakes that have been engineered to be more efficient, lighter, and more compact. Our angle-port brakes use a proprietary gas-trap design which reduces the amount of propellant that escapes back through the muzzle.

 The traps operate as a 'one-way' gate to help redirect and vent more propellant than a standard open port brake. The following cross-section illustration shows gas The KA angle-port brakes utilize this gas trap setup to direct gases away from the bore, redirect them, and prevent them from deflecting back into the bore. This "slingshotting" of the propellant results in much higher exit velocities and greater recoil reduction. The lighter design of KA angle-port brakes also makes them more manageable for general use, even allowing their use on smaller carbines.

Now that we've covered what causes recoil and how muzzlebrakes counteract it, lets discuss how that benefits the user.  When firing a rifle, there should only be three main concerns:

Sight picture- Focusing on the target.

Proper stance/position and trigger pull- Being in a steady position to support the rifle and proper trigger finger placement and pull.

Proper breathing- Being relaxed and not panicky when firing. Heavy breathing results in moving the rifle and possibly missing the target. At a competitive level, proper breathing can make the difference between first and last place.

When firing a rifle with substantial recoil, many shooters will be subconsciously anticipating the recoil. This causes that involuntary flinch that you experience all too often. With a powerful rifle, this flinch will often get worse after a couple rounds once your shoulder gets sore. Recoil can keep you from shooting to your potential and can also keep you from practicing as much as you should. All of us have bought a rifle that we like but kicks a little too much to be comfortable, a proper muzzlebrake solves this problem by reducing the recoil to a more comfortable level. When you pull the trigger you should only be thinking about hitting your target, not worrying about how hard your gun is hitting you. A good muzzlebrake can make your rifle a lot more enjoyable to shoot and let you spend more time at the range with it. On a demo day at the range, each of us here at KA might shoot 50+ rounds of 300WinMag or other high-power rounds and each of us come home unbruised and unshaken, even with a 15lb rifle you're not going to get that same level of comfort.

Thanks for spending some time with us on this topic, hopefully this information was beneficial to you