What Makes Recoil?

I was in a gun shop a day or so ago. For those who know me, this is not a shock, but I digress.

Here on my right was a gentleman who was looking at one of the ultra-small .380 ACP handguns and the subject of ‘recoil’ came up. His question was pretty simple, “Do heavier bullets give more recoil?”

The answer is not so simple. One of the laws of the Universe, like gravity, magnetism or women.

The short answer is “Yes, most of the time”. Heavier bullets will give greater recoil if all other factors remain the same. Especially velocity. However, normally changing one portion of the situation will mandate a change in others. In most firearms, changing to a heavier bullet results in a lessening of the velocity.

Before we start talking about that, I’m going to interrupt this line of thinking and introduce a basic concept: There are two kinds of recoil. Yup. Two kinds. There is actual recoil and perceived or ‘felt’ recoil. Now for a bit of near-heresy: Perceived recoil causes more problems than actual recoil.

Okay. ‘Actual’ recoil is the physics calculated movement of the firearm in response to the forward movement of the bullet. This is Newton’s Third Law of Motion. When bullet go that way, gun come this way. The formula is to multiply the mass of the bullet by the velocity of the bullet and then divide this product by the mass of the firearm. By the way, mass and weight are not exactly the same; but in a single and isolated gravity field – like that of Earth – we can pretend they are. However, this is not the whole story.

Perceived or felt recoil is what the shooter notices or feels when firing a given firearm. This can be influenced by a multitude of factors. Putting ‘rubber grips’ on a heavy recoiling revolver or a recoil pad on a rifle or shotgun is one such factor. Even though the firearm is the same and the round fired is the same, the recoil is perceived as less. This is because the grip or pad compresses during recoil. This compression spreads the recoil energy out over a longer period of time and cushions the blow of recoil.

Narrow stocks and butt pads on rifles or shotguns concentrate the recoil into a smaller area. This tends to make the recoil seem more forceful. Wider stocks and butt plates spread the force over a larger area and makes the recoil seem less forceful.

In my experience teaching people to shoot, report, muzzle blast, the noise of the firearm discharging, is far more disturbing to the shooter – especially a new shooter – than mere recoil. Muzzle blast hurts – actual pain – the ears more than recoil hurts the hands and arms from knuckles to shoulder. The one single thing one can do to shoot better and make shooting more fun is to protect one’s ears. Or the ears and hearing of a prospective shooter.

However, what about changing bullet weight?

A normal .45 ACP load with 230 grain bullet runs about 850 fps to duplicate the U. S. military ball loading. Therefore, multiplying the mass of the bullet times the velocity and dividing by the mass of the pistol, the recoil force is calculated as follows:

230 grain bullet, divided by 7000 grains per pound equals 0.03286 pounds.
Multiplying 0.03286 pounds by 850 feet per second equals 27.931 foot pounds (momentum, not kinetic energy.)
Dividing this product by the weight of the pistol – 2.44 pounds, according to the Wikipedia article – results in a recoil velocity of the pistol of 11.45 feet per second.

Since the bullet starts at rest, the average speed of the bullet in the barrel is 425 fps. Dividing the velocity of the bullet by the length of the barrel, rounded off to 4.25 inches, the bullet takes a time of 0.0008333 seconds from ignition to leaving the muzzle. This is the amount of time the recoil impulse is being delivered to the firearm. Therefore, the standard load for .45 ACP in a Government Model delivers 11.45 f/s in a period of .0008333 seconds.

Some will read the prior paragraph and think, “Wait! The barrel length of a Government Model or M1911 is FIVE inches, not 4.25. He must be using a Commander version!” No. This is a Government Model. From an internal ballistic standpoint, barrel length is the distance during which the bullet is being pushed by the expanding gases; it is measured from the base of the bullet to the muzzle. The commonly used measurement for barrel length is the holster maker’s standard. For pistols, from the breech face to the muzzle and revolvers are measured from the front of the cylinder to the muzzle. A quick consideration will lead to the conclusion that pistols always have an internal ballistics measure LESS than commonly thought, and revolvers always have an internal ballistics measure MORE than commonly thought. I digress, in a fashion.

I once developed a load for a standard .45 ACP Government Model that clocked at about 1100 fps on my chronograph. Yup, 1100 fps. The rest of the story is it used a 155 grain bullet. By the time I had enough pressure to work the slide reliably, the velocity was around 1100 fps. What was interesting – other than the great reaction of other shooters when I shared the information – was the recoil. It was not brutal and over powering, but it was very abrupt. Running through the same algorithm I did for the 230 grain load a couple paragraphs ago, this load delivers 29.601 foot pounds of momentum, 12.13 f/s of recoil velocity and the recoil pulse lasts 0.0006439 seconds.

Subjectively, I find the recoil of the lighter bullet less than the standard load. It isn’t, according to the numbers. However, the lighter bullet recoil lasts roughly only three-quarters as long as the standard load.

What does all this mean? Well, for one thing, bullet weight isn’t the whole story.

I’m going to change the issue now.

One of the hardest recoiling guns I remember shooting was a Smith and Wesson 1950 Target Model. That revolver is a six and one half inch, thin barreled affair chambered for the .45 ACP or AutoRim cartridge. Normally, a .45 ACP is not considered a fearsome recoiling round. (At least not to me; there are those who find it so, but they’re sissies.) This particular revolver had an exposed back strap. The grips were full and properly fitted, but did not have the rubber flange found on some grips to cover the back strap of the grip frame. (My hands are small.) Shooting full standard loads in that revolver and seriously focusing on precision target work, that revolver hurt to shoot after three or four cylinders of ammunition.

I still shoot a Smith & Wesson 29-2 .44 Magnum revolver. The common load I shoot in that revolver develops much more recoil than the .45 ACP ammunition of the last paragraph. (It’s a 240 grain bullet at just over 900 f/s.) However, the 29 doesn’t cause the same recoil pain of the 1950 target model. The weight of the two revolvers is fairly close. The grips are different. To the best of my memory the 1950 Target Model had basic wood grips in the manner of Herrett Shooting Stars. The 29 I currently have sports stag grips with Tyler T-grip inserts.

Jumping to ‘other’ pistols, Glocks seem to be very recoil dampening. My take is the plastic grip frame flexes and absorbs recoil when the pistol is fired. I remember firing a Glock in 10 mm caliber, using factory loads. The recoil was sufficient to note one had fired a shot, but the level of recoil was nearly disappointing after all the hype I had read regarding the recoil of the 10 mm cartridge.

Then there are rifles and shotguns. In the early days of rifles, muskets, ‘gonnes’ and so forth, the stock was built with a fairly severe bend at the rear of the firing mechanism (the ‘action’, it’s called). This was done so when the shooter mounted the firearm to the shoulder, the barrel (and later the sights) was in line with the shooter’s line of sight. This made sighting easier, but the recoil of the firearm tended to rotate upwards about the shoulder. Since the early firearms were powered by ‘black powder’, the thrust of recoil was rather slow by modern standards, the firearm was heavy (to contain the pressure of the powder burning) and therefore ‘recoil’ was manageable.

As time went on, black powder was refined and developed more energy. Then smokeless powder was invented and adopted for common use. As a result, calibers became smaller and velocities became faster. The net result was the old stock design tended to recoil into the face of the shooter. This action of being slammed in the face by the cheek piece of the rifle or shotgun make ‘perceived’ recoil greater and more objectionable. Probably some of the worst offenders were the Winchester lever rifles. “Rifle” style butt plates, the crescent shaped type with the points top and bottom, were seriously vicious if mounted to the shoulder wrong. Which is probably why only ‘shotgun’ (flat) butts have survived.

The AR-15 (or militarily, the M-16 and so on) has a ‘straight line’ design. The idea is to reduce muzzle climb by directing recoil directly to the rear. That’s why the rear sight is perched up on that so-called ‘carrying handle’.

So what makes recoil? A number of things. Among them, bullet weight. But as many things in life, that’s not the whole story.

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