Recoil: A tale of three measurements

Recoil is a familiar term and topic in this blog. I’ve mentioned it in passing within posts discussing firearm or cartridge selection and also in posts talking about skill development. I’ve even dedicated posts to the topic in the context of a particular cartridge which include a few numbers. However, I haven’t dedicated any time to explaining what those numbers measure or how they can be interpreted until now.

Why now? Long time readers know I’m a fan of shooting big bore handguns and I had the opportunity to shoot one while also introducing a friend to them yesterday. More specifically, we shot a few 700 grain 500 S&W Magnums from this S&W revolver. While it was fun, my hands are reminding me of yesterday’s events as I’m writing this so this topic is fresh in my mind.

First things first, most folks tend to associate the muzzle energy number printed on ammunition boxes with the recoil produced by the cartridge. I’ve done this. On the surface, this association makes sense since larger muzzle energy numbers are indicative of how powerful the cartridge is. As such, it’s natural to think that a larger muzzle energy value is associated with more recoil. However, there are a lot of other factors beyond the cartridge itself that affect the amount recoil produced and how the recoil is felt or perceived. Furthermore, perceived recoil can also be rather subjective. That said, there are some objective measurements we can use to give us an idea of the recoil one will experience.

Before getting into the numbers, let’s talk about the variables for recoil calculations. There are four variables that are necessary: bullet weight in grains, bullet velocity in feet per second, powder charge weight in grains, and firearm weight in pounds. Good bullet and firearm weight measurements are the easiest to obtain as they can be taken directly from the manufacturer. Bullet velocity should be measured using a chronograph to get a good value as printed materials tend to be optimistic for marketing purposes. However, the velocity from marketing materials can be good enough if we are looking for a general idea of recoil rather than a precise recoil measurement value. Powder charge weight takes the most foot work unless one happens to be hand loading their own cartridges. Ammunition manufactures will rarely provide charge weight values as it’s part of their secret sauce. However, we can still use charge weight values from load data manuals as a good enough value to get that general idea of recoil values. In fact, I’m going to make use of Nosler’s online load data as the source for this post. I’m also going to plug those values into the recoil calculator provided by ShootersCalculator.com.

Recoil Energy

Recoil energy, measured in foot pounds (just like muzzle energy), measures how powerful the recoil will be. This does very little to describe what the recoil will feel like, but it can provide a little insight into how much effort a shooting will need to exert in order to get the gun back on target for a follow up shot.

For example, consider shooting a .40 S&W cartridge from a Glock 23 which weighs about 1.67 lbs. A typical bullet will weigh 180 grains. Assuming a charge weight of 5.9 grains and a muzzle velocity of 1034 fps, we end up with a recoil energy value of 8.85 ft-lbs. The exact same cartridge from a Glock 22 which weighs about 1.78 lbs yields a recoil energy value of 8.3 ft-lbs (assuming no change in muzzle velocity). The difference in recoil energy supports the common notion that a larger pistol is easier to control and shoot.

There is no doubt that a reader will point out that the .47″ larger barrel of the Glock 22 makes the difference in recoil energy too optimistic because that 180 grain pill will have a faster muzzle velocity out of the Glock 22 and the reader would be correct. However, I’m only trying to illustrate the point that a heavier pistol will dampen the recoil energy making it easier to control. This is one reason many competitive shooters will opt for heavier framed pistols.

Let’s consider shooting a 10mm cartridge from a Glock 20 which weighs about 1.91 lbs. A common bullet weight will also be 180 grains. However, this time we are looking at a charge weight of 9.2 grains and a muzzle velocity of 1267 fps. The result is a recoil energy value of 12.49. Comparing that to the 8.3 ft-lbs of the .40 S&W from the Glock 22, we can conclude the 10mm from the Glock 20 results in more powerful recoil and therefore will require more effort to control.

Recoil Velocity

Recoil velocity, measured in feet per second (just like muzzle velocity), measures how fast the recoil travels at the shooter. This measurement can be used to describe how the recoil will feel. Not so much in terms of discomfort and pain, but rather whether the recoil will be fast snap or slow push.

To illustrate this, let’s consider shooting a 9mm in a Glock 19 versus a .45 ACP from a 1911. I’m using this example because folks generally describe the recoil from 9mm as snappy and the recoil from .45 as a thump. The inputs from the 9mm in the Glock 19 are as follows: 124 grain bullet, 1145 fps bullet velocity, 7.9 grains charge weight, and 1.48 lbs firearm. The inputs from the .45 ACP 1911 are: 230 grain bullet, 916 fps bullet velocity, 7.3 grains charge weight, and 2.6 lbs firearm. The recoil velocity of the 9mm is 17.52 fps whereas the recoil velocity from the .45 is 13.56 fps. Knowing that folks are going to ask, the recoil energies are 7.06 ft-lbs and 7.45 ft-lbs respectively.

What can we take away from this? Well folks who have shot both of the cartridges in the pistols used for the calculations should quickly see how the difference in recoil velocity relates to how the recoil feels. If one hasn’t had the chance to shoot these cartridges and pistols, then note the difference between recoil velocities is noticeably greater than the difference in recoil energy. While .45 recoil energy is greater there isn’t a significant disparity in how powerful the recoil is between the two cartridges and pistols. On the other hand the disparity between recoil velocities indicates the recoil will feel characteristically different where the faster velocities are more snap and the lower velocities are more shove.

Another interesting thing to point out is that muzzle energy of these two cartridges, 361 ft-lbs for the 9mm and 429 ft-lbs for the .45 ACP, indicate a 15% difference in muzzle energy. However, due to the difference in charge weight and firearm weight we only see a 5% in recoil energy. This should help illustrate the limitation of associating muzzle energy with recoil.

Recoil Impulse

Recoil impulse, measured in pound seconds, measures the force applied over a period of time. I tend to think of this measurement as the ouch factor where a greater impulse means a greater ouch. However, this number can be misleading because the calculation is not affected by the weight of the firearm (I’ll illustrate this shortly). So perhaps, one can be better served by thinking of this measurement as the ouch potential. One thing I can tell you is that the greater the force over a shorter period of time generally sucks and leaves a mark.

Before I get a head of myself, let’s look at the recoil impulse of the cartridges so far. The 9mm load we considered had a recoil impulse of 0.81 lbs-sec, the .40 had a 0.96 lbs-sec impulse, the .45 had a 1.1 lbs-sec impulse, and the 10mm had a 1.22 lbs-sec impulse. Generally speaking, I’ve found that I become fatigued faster by shooting cartridges with a larger recoil impulse. I also tend to experience more bruising and soreness when shooting cartridges with greater recoil impulses.

Now let’s consider a hot .44 Remington Magnum load with 240 grain bullet traveling at 1577 fps using a charge weight 23.2 grains. That yields a recoil impulse of 2.2 lbs-sec. Most folks will likely agree that a hot .44 magnum load has a higher ouch factor (or potential) than any of the other cartridges we’ve looked at. At the same time, folks will also say the ouch will be greater for a lighter revolver than a heavier one. Let’s consider the Smith & Wesson 329PD which weighs 1.58 lbs versus a Smith & Wesson 629 which weighs 2.59 lbs (both of which have a 4.125″ barrel). The difference in weight results in 44.71 fps recoil velocity and 49.08 ft-lbs recoil energy from the 329PD versus 27.27 fps recoil velocity and 29.94 ft-lbs recoil energy from the 629. So while the .44 cartridge has a recoil impulse value of 2.2 lbs-sec, the 329PD experiences results in significantly snappier recoil and a lot more recoil energy to contend with than the 629. Either way, some bruising and soreness can be expected from both.

There is something we can do to dampen the recoil impulse and therefore reduce bruising, soreness, and fatigue. That is to introduce materials that compress between the shooter and the firearm. For a handgun, this comes in the form of rubber grips. For a rifle, this comes in the form of a recoil pad. What both of these things do is reduce the recoil impulse by effectively increasing the period of time it takes for the recoiling force to be transferred from the firearm to the shooter’s hands or shoulder. Unfortunately, the math used to calculate recoil impulse doesn’t take this into account.

Putting It Together

To recap, recoil energy gives us an idea how powerful the recoil is. Recoil velocity describes how snappy the recoil is. Recoil impulse describes how likely the recoil is to cause fatigue or leave us bruised and sore. I’ve also mentioned there is something we can do to dampen recoil impulse. What I haven’t mentioned is there are a number of other things that we can do to mitigate recoil. For instance, a muzzle break, compensator, or even barrel porting can be used to redirect the direction of the gasses leaving the barrel and thereby reduce the resulting recoil velocity. For rifles, we can use shooting bags to stabilize the rifle and also mitigate recoil. However, these accessories and techniques aren’t reflected in the recoil calculations. However, that doesn’t mean the calculations aren’t helpful. Rather they can help us decide how much value there is in taking recoil mitigation measures and investing in recoil mitigating accessories and modifications. While the numbers can’t tell you exactly what the recoil will feel like, they help one prepare for the initial experience and thereby reduce the chance of injury.

Before closing, I’m going to provide a short table of some common pistol cartridges and another containing some common rifle cartridges. I will also briefly share how I interpret those numbers. Let’s start with the pistol cartridges.

Let’s walk down the table. Comparing the 9mm and the 40 S&W we can see the recoil from the 40 S&W is greater with about the same snap. The impulse of the 40 S&W indicates the possibility of faster fatigue and discomfort. The 45 ACP on the other hand has less power and snap than the 40 S&W, the additional impulse indicates the possibility of even greater fatigue and discomfort. The 10mm’s numbers suggest more powerful and even snappier recoil with the possibility of even more fatigue and discomfort than the other cartridges thus far. The 357 Magnum appears to have slightly more powerful recoil but less snap than the 10mm while increasing the likelihood of fatigue and discomfort. Finally, the 44 Magnum dwarfs all the other cartridges in terms of recoil power, snap, and potential discomfort.

Let’s look at some rifle cartridges now.

Let’s walk down the rifle cartridge table now. Starting the 223 Remington, it’s hard not to notice that the recoil energy and velocity is lower than any of the pistol cartridges we explorer while the recoil impulse is in between the the 10mm and 357 Magnum. There is an explanation for this. Remember that recoil impulse doesn’t take the firearm weight into consideration and while an AR-15 is several times heavier than any of the pistols mentioned the 223 Rem is the most power cartridge we have looked at. So the potential for fatigue from the cartridge is greater. However, the weight of the AR-15 significantly dampens the recoil energy and velocity making it a cartridge that is very easy to manage with negligible snap. In contrast, the 308 Winchester ups the recoil power game with a mild shove and a noticeable impulse that can leave the inexperienced shoulder a little sore. The 30-06 Springfield cranks up all the numbers again which is consistent with several folks who often describe this cartridge as having a good kick. The 300 Winchester Magnum has left its mark in the form of a healthy bruise on many shoulders. The 7mm Remington Magnum’s recoil numbers land pretty much in between the numbers from the 30-06 and the 300 Win Mag. Finally, the 270 Winchester’s numbers are very similar to those from the 308 Win.

Again, these calculations only help paint a picture that can help a person get an idea of the recoil to expect with a particular firearm and cartridge combination. They also do a much better job of painting that picture than attempting to correlate muzzle energies with recoil. However, the numbers are just numbers and one can’t really know the recoil until they experience it for themselves. I hope that by sharing this measurements and how to obtain them folks will be able to better prepare themselves for experiencing a new cartridge or firearm for the first time safely resulting in a good, fun, and memorable experience.