# Hand gun physics

When you watch a video of someone shooting a handgun, or if you have ever shot one yourself, you notice two things immediately:

1. the gun has serious kickback, and
2. the gun’s finishing position is usually pointing upward, and the shooter has to bring the barrel of the gun down to a level position again before taking another shot.

My question: The hammer hits the firing pin, and the firing pin hits the cartridge to ignite the primer in the bullet casing, which causes the bullet to be propelled out of the gun. Since Newton tells us that every action has an equal and opposite reaction, the power that thrusts the bullet forward results in the shooter’s arm to take the recoil energy, almost always resulting in the arm and gun moving upward.

Since this happens instantaneously, why doesn’t the bullet take a slightly upward trajectory as it exits the barrel? It seems that when aimed properly, the path of the bullet is not changed at all and the shooter can hit a target in front of him. But why? Is the speed of the bullet so fast that the recoil doesn’t occur until after the bullet clears the barrel?

I am not clear as to why the arm would not begin its upward movement the instant the bullet is fired, BEFORE it exits the barrel. Even if it was a small fraction of distance that the arm travels upward, it should impact the bullet’s flight path, correct? Or does the shooter have to take that into account as he aims? Or is the distance so small as to not have an effect (i assume this is the answer, but given the recoil, it seems counter-intuitive to me.)

Thanks.

The barrel and slide assembly go directly back against the recoil spring, which accounts for the equal and opposite reaction of the first fraction of a second after the gun is fired. The rest of the body of the gun, and then onto the shooter’s hand and arm, doesn’t start being pushed against substantially until the slide has reached the rearward end of its journey.

A 9mm round for example travels at about 1200 feet per second - so it will clear a 4 inch barrel in about 1/3600th of a second, or roughly .0002 seconds. I would guess that the slide is barely on its way back by the time the bullet leaves the barrel.

It does. Well, sort of.

A lot of people don’t know this, but if you were to mount a handgun in a vice that is mounted to a sturdy table, and you carefully line up the sights to the target and fire a shot, the bullet will not hit the target. It will hit low. If you then remove the gun from the vice, and shoot the gun using your hands, the bullet will hit the target (assuming you’re an experienced shooter).

Why? When you shoot an handgun using your hands, the barrel will rise between the time the bullet exits the chamber and the bullet exits the muzzle; the barrel rises as the bullet travels down the barrel. Handgun manufactures know this, and thus the sights are designed accordingly.

When you are shooting a handgun with your hands, and with the sights lined up to the target, the barrel is pointing “too low.” After the bullet exits the chamber, the barrel rises to the point that the barrel is “on target” (or slightly higher to allow for a proper trajectory). So when you shoot a handgun, never try to fight barrel rise, else your shots will be consistently hitting too low.

It should also be noted that this effect is much more pronounced in revolvers than semi-auto handguns.

This is a slow-motion video of a pistol being fired. It shows pretty clearly what SenorBeef was talking about. You can see the slide start to move back pretty much immediately but the entire gun doesn’t really start to pivot upwards until the slide reaches the end of its travel.

Compare that to this video of a revolve being fired. Since there is no slide to move, the entire pistol does start to pivot upwards immediately.
You can also see how quickly, in both cases, that the bullet exits the barrel compared to how fast the other things all move. Even in the revolver's case, the gun doesn't have much time to pivot before the bullet is already gone.

How much difference does the vice make as opposed to holding the gun with one’s hands?

Stink,
What makes you think that the bullet being propelled out of the gun happens instantaneously as opposed to really fast for the scale we’re used to?

Okay, but why does the gun get forced up, and not down?
Newtons law says “opposite” directions. As the bullet flies straight down the barrel, that should create a force directly backwards, not upwards.
The force is, of course, resisted by your arm and shoulder muscles.
But I can move my arms up OR down, pretty much with equal ease and effort. Why doesn’t the gunshot tend to push the shooter’s arms downwards?

The barrel is above the center line of the gun, so it rotates that way. If you were to shoot a gun upside down, the barrel would recoil the opposite. Or if you built a gun with the barrel along the bottom below the center point it would recoil downwards.

I suspect it’s ergonomically easier to handle upwards recoil. Most rifles push the cast majority of their recoil straight back.

The backwards force get transformed into partial upward force because of the anatomy of the human body and the way the gun is typically held.

The recoil pressure is applied at a spot which is higher than the hinges of body which are involved; the wrist and elbow joints.

If you held the gun upside down (by twisting your hand 180 degrees), the gun would point downward.
In the same way, if you shoot right-handed, the gun tends to point right because the pressure is applied to the right of the swivel point (the waist/spine). If you shoot lefty, the gun tends to point left.

Senor beef may be able to supply info here: because I’ve only fire rifles that had a stock and I used it: What happens when a rifle lacks a stock or is fired without using it? I thought the reason rifles don’t go up much was 1) they’re heavier compared to what is propelled 2) they have better dampening and (relevant here) 3) the stock puts the pressure on the torso, thereby largely bypassing the wrist and elbow joints as hinges.

[quote=“SenorBeef, post:7, topic:698477”]

The barrel is above the center line of the gun, so it rotates that way. If you were to shoot a gun upside down, the barrel would recoil the opposite. Or if you built a gun with the barrel along the bottom below the center point it would recoil downwards.[/QUOTE

There’s an interesting possible RL historical application of this. I’ve heard that the Chinese, using their version of the broomhandle C96 Mauser pistol, would fire it on its side (“gangsta-style”) so that the recoil would cause it to sweep horizontally.

Great cite there, ECG. The bullet is gone before the slide even starts to move, let alone the shooters arm starting to move.

Recoil movement happens after the bullet is well underway and the gas that pushes the bullet widens out somewhere 12-15 inches from muzzle. This widening or expanding of the gas reacts against the air.
The video the good Engineer linked to needs to be watched frame by frame to see this happening.

This is not true. Recoil begins the instant the bullet begins to move.

It all depends on the gun. Here’s a video of a 1911. Starting at 2:16, you can clearly see the slide move before the bullet exits the muzzle.

As I stated above, the muzzle rises as the bullet is going down the barrel. (It doesn’t need to rise much to affect accuracy; just a half a millimeter of muzzle rise on a gun with a 6" barrel will raise the POI 3 inches at 25 yards.) The magnitude of rise depends on lots of factors: distance between sight axis and muzzle axis, length of barrel, speed of bullet, firmness of grip, etc. On some guns, it is next-to-impossible to see the rise with a camera, due to the magnitude of the rise being so small. The effect tends to be more pronounced on long-barreled revolvers. For an example, check out this video and do the following:

1. Make the video full-screen.
2. Turn off the sound.
3. Put it in pause mode.
4. On the first frame, put a piece of tape on your monitor at the bottom of the muzzle.
5. Play video over and over during the first second. You will see the muzzle rise before the bullet leaves the barrel.

And this is why the front sight on many revolvers is higher than the rear sight - when you squeeze the trigger, the barrel is pointing too low. As the bullet accelerates down the barrel, the muzzle rises. When the bullet exits the muzzle, the angle of the barrel is the correct angle for the bullet to hit the target.

Here’s another video of shotguns. Loop it between the 9 s and 11 s points. Definite recoil and muzzle rise before the bullet leaves the barrel.

Thanks for posting these great videos.

The first video seems to demonstrate what SenorBeef was describing. Even slowed down, it looks like the bullet is well past the barrel before the gun starts its upward swing, and the reason is because the slide and spring seem to absorb the backward force.

However, the revolver video seems to show the gun moving slightly upward before the bullet reaches the end of the barrel. Is this what everyone else sees? And is this enough to prove what Crafter_Man stated? I had no idea the manufacturer adjusted the sites for this phenomenon, but it does make sense.

Again, it depends on a number of factors. If the barrel is short, and if the bullet velocity (while in the barrel) is very high, and if the sight axis is very close to the barrel axis (such as is the case with my S&W M&P), and if you have an extra-firm grip, then muzzle rise will be negligible while the bullet is accelerating down the barrel. It won’t be zero, but it will be so small that you can’t measure it using a camera.

I was wondering, the revolver movement, could any of that be due to the shooter?

When he flexes to pull the trigger, could that have caused some movement?

An interesting phenomenon about revolvers illustrates that the barrel actually rises while the bullet is traveling down the barrel, as Crafter Man explains. Many revolvers can accommodate different loadings, resulting in lighter and heavier bullets and faster and slower speeds. While those more familiar with rifles would assume that a slower bullet would impact lower than a faster one, the opposite is generally true at relatively short handgun distances. If you sight in your .44 magnum at 25 yards using light 200-grain bullets, it will shoot high at 25 yards when shooting slower, heavier 240- or 300-grain bullets. The reason is that the slower bullet is in the rising barrel longer, and leaves when the barrel is tipped up just a tiny bit more. Now, after 50 or 100 yards, the slower bullet will start dropping more than the lighter one.

As mentioned, the rising handgun is more pronounced with revolvers than pistols due to the design and geometry of the two types of handguns. Also as mentioned, the backwards force gets translated to rotational force due to holding a handgun below the horizontal plane of the barrel.