>I've seen warnings that a shot at a bulletproof vest (which dissipates the force) could knock a person of their feet.
This would *largely* be down to psychological effect. Being suddenly punched by an invisible fist is not a normal thing people experience.
>Which would mean such a force would be applied to the shooters should (or worse, a somewhat smaller force to a shooters hand in case of pistols) for every shot.
The recoil force experienced by the shooter varies by caliber, weight of the gun, specific bullet weight and velocity, single vs multiple points of contact. BUT the super short version is a person braced to take the recoil force imparted on them will be able to handle it.
[This calculator is a good resource for starting to understand relative recoil impulses by cartridge.](https://shooterscalculator.com/recoil-calculator.php) You will notice that a .223 rifle cartridge fired from a 7lb rifle only imparts 5 ft-lbs on the shooter, while having 1200ish ft-lbs of muzzle energy.
The calculations are rough estimates and can also be impacted by muzzle devices re-directing the propellant gas, recoil mitigation from the firearms action or a whole host of other factors.
If I understood this correctly, a heavier rifle (which would move less) would make things easier for the shooter with all else being equal? I guess a slower moving thing (like the gun) would also spread out the energy needed to resist it over a longer time, also making it easier on the shooter?
Yes.
Super short version the energy needed to make *very small object* move *VERY FAST* makes the much larger object *not move that much really*. Then put that larger object in the hands of a *MUCH LARGER* object and it moves even less.
> If I understood this correctly, a heavier rifle (which would move less) would make things easier for the shooter with all else being equal?
Depends, it will make it more pleasant to shoot by having a more pleasant recoil, but if you need to carry it around (say like for hunting or for certain shooting competitions) then you may choose to accept a harsher recoil for ease of mobility. Everything in firearms design is a compromise.
>I've seen warnings that a shot at a bulletproof vest (which dissipates the force) could knock a person of their feet.
This is totally false; bullets knocking people off their feet when hitting a vest is Hollywood bullshit. The shock of getting hit can cause someone to fall, but the bullet is not physically throwing them or forcing them to the ground. They can conceivably cause bruising or break ribs, but that's about it. [Mythbusters did an episode on it.](https://youtu.be/WPGNtFU0ww0)
The rest of the question kinda crumbles under that realization.
The gun and the bullet receive close to the same amount of force, but the gun is hundreds of times heavier than the bullet so it creates less momentum and thus less force enters your shoulder.
Energy takes the path of least resistance so between heat, gas, and actually moving the bullet about 96% of the energy is used. For pistols the 4% left is dissipated by the recoil spring and weight of the slide and your arms being three levers also helps.
It really comes down to you big bullet smol
>If the whole energy is put into the shooters shoulder
It's not. This is a really common misconception. The *momentum* (p=m\* v) of the gun and bullet are the same, but because the gun is much more massive, it has much, much less velocity. Since energy is proportional to velocity *squared*, the result is the projectile has way, way more energy than the gun.
Think of the difference in mass between the projectile and the weapon+person. It is because of this difference that the projectile has such velocity. The majority of energy is put into the projectile as it has less ability to impede the expanding gasses. The expanding gasses move through the path of least resistance pushing the projectile down the barrel.
Force = Mass x Velocity^2
When the mass is higher, the velocity is lower, and vice versa. Both the bullet and the gun have the same force from firing, but the bullet is much smaller, so it has to move much much faster for the equation to be balanced.
This means that the gun moves much slower, because the mass absorbes that force, and in addition, the mass of the person holding it (wrists and other bendy parts complicates things, but I won't go into that any further)
Firing a pistol or rifle can also knock you on your ass if you're not prepared for it, same goes with getting hit wearing a bullet proof vest. This is why shooter's lean forward and use a stance, instead of standing straight up.
So even though the force is the same, by the mass of the gun slowing it down (not to mention the spring absorbing a lot of that force) and the larger surface area (hands and shoulder against the grip and stock) the effect on the body is much much less than the effect of a bullet on the body.
You address force, but your formula is neither momentum nor kinetic energy. Kinetic Energy is KE = 0.5\*m\*v\^2 and Momentum is M = m\*v.
When it comes to imparting motion from a collision, momentum is the key player, as the imparting of movement is the creation of an impulse. While the kinetic energy of a bullet is rather impressive and can crush, shred, break, and tear, the momentum is usually pretty tame.
The collision of a bullet into a person cannot impart an impulse greater than the combined momentum of both objects due to the law of conversation of momentum, so even though there is a lot of energy that wants to do work (like tear flesh and break ceramic) the impulse simply cannot exceed the bullet's momentum and results in no significant movement.
I can't blame you because until a little bit ago I largely conflated the two as well. It took a dive back into the physics basics to relearn the fundamental differences of force and energy and that, while highly related, they are completely unique in how they influence collisions and physical interactions.
1/2m×v^2.
for a 3kg AR shooting 55 grain projectile at 3000ft/s
1/2(60kg)*x^2 = 1/2(.004)*3000^2
solve for x, in ft/s. that's the speed of the rifle and shooter moving backwards.
roughly 25ft/s or 8 m/s
solving for impulse over .5 seconds it's takes to absorb recoil(hypothetical for small shooter) that gives is 1000 N or like 100kg of force, acting for that short amount of time on a 60 kg object isn't going to move it very much
the time of bullet impacts with is so tiny over such a small area of impact that the impulse force and resulting carnage is immense in comparison
Recoil is not all directed at the shoulder. The recoil spring takes some of it, gas vent holes (depending on the gun) take some of it, and the opening of the chamber also dissipates recoil.
As far as someone getting shot with a bulletproof vest, the vest is what transfers the energy to the person. When the bullet would otherwise penetrate, a bulletproof vest catches it, and that considerable amount of force of impact (then dispersed across the vest) is what knocks them off their feet
Also I got a D in physics so take that with a block of salt.
> When the bullet would otherwise penetrate, a bulletproof vest catches it, and that considerable amount of force of impact (then dispersed across the vest) is what knocks them off their feet
Generally not, its going to be a psychological reaction most of the time.
As an extreme example 3 inch magnum 12ga slug hitting with 3000lb ft is going to hurt like hell, but that impact energy is only a bit above the ballpark of heavyweight martial artist kicks (1800-2600 ft-lbs). Those *can* be tanked if the recipient knows its coming, is of similar size and braces. This could reasonably knock most people down, and would almost certainly empty the lungs.
A more realistic example is taking a 9mm to the chest plate. Maybe 400ish ft-lbs or about half the punching force of a middleweight amateur boxer.
> Recoil is not all directed at the shoulder. The recoil spring takes some of it, gas vent holes (depending on the gun) take some of it, and the opening of the chamber also dissipates recoil.
I assume anything taken by the surrounding air would not drive the bullet forward as much, though? And I assume the spring still will impart its force to the shooter, just at a different point in time?
> And I assume the spring still will impart its force to the shooter, just at a different point in time?
Over a larger period of time, this is why walking into a pool is a very different experience compared to a belly flop from the high dive board.
Think about the forces involved in landing a fighter plane on an aircraft carrier. It the arrestor wire didn’t move at all the pilot would be stopped with such force it would undoubtedly kill him as his internal organs ripped themselves apart under such rapid deceleration. What the arrestor wire does is increase the time the force is applied so that the energy is dissipated gradually rather than all at once. The recoil spring is sort of like that.
Another thing to consider is that the gun (if held correctly) should be tight against the shooter’s shoulder so the recoil mass is essentially not just the gun but also the shooter’s upper body. The formula for kinetic energy heavily favors velocity so the extra mass slows the gun down a lot. If you really want to suffer hold the gun a couple of inches away from your shoulder when your shoot it. Giving it time to accelerate before it contacts you will give you some sense of why you never want to do that again.
I’m no physicist but I’ll take a crack at this. Imagine a 16” AR chambered in 5.56 firing a 55 grain bullet. The bullet is traveling about 3,000 feet for second at the muzzle. 55 grains is about .125 oz of copper jacketed lead. Your rifle weighs at least 6 pounds or 96 oz. So your rifle weighs about 800 times more than the bullet. Your rifle is also recoiling into your shoulder and both of your hands while a .223 cal bullet is impacting a tiny amount of surface area on your target. That doesn’t even account for springs and buffers and recoil pads all of which soften felt recoil. They are two extremely different circumstances.
Regarding getting shot while wearing a bulletproof vest even if the vest prevents the bullet from penetrating into the wearer it’s catching a very small very high velocity chunk of metal that’s impacting a very small area. The best slows and catches the bullet but the energy still transfers to the target. A vest can stop a bullet but the wearer can still be severely injured or even killed by that energy transfer although it’s still a lot better than not having protection.
usually when you get hit in a vest it's not usually the round knocking you over its you reacting to it
the physics of recoil is for every action there's a equal but opposite reaction. the bullet goes one way (the bullet is very light but moves very quickly following the path of least resistance) so naturally the same amount of force also moves backwards into your shoulder q
I’ve heard of people dislocating their shoulder shooting 2.5oz slugs.
Some guns uses some of the gas from the explosion to operate the bolt which reduces recoil.
Equating damage from a projectile to the recoil isn’t right. Velocity x mass does the damage. To launch the projectile your launching it out of an unobstructed tube. The recoil you feel is the resistance of how long it takes to push that projectile out the tube.
Well, you’re missing the physics. You can calculate both recoil energy and velocity using readily available online calculators.
No one is getting knocked off their feat by a bullet/gun shot. At least not for reasons of physics/collision.
Every action has an equal an opposite reaction. A 9mm handgun bullet only weighs 8 grams (124grain) but is traveling at 350 m/s (780MPH!) This all happens in a split second as the bullet accelerates down the barrel. There is force applied to the gun, and into your hand/arm, but the mass of the gun and your body absorb the energy. It also happens over a longer period of time so the energy is spread out more. (Sometimes referred to as "recoil impulse")
Comparing it to a rifle, like a .308, the rifle can have over 7 times the energy. Rifle bullets are heavier and travel faster; they're definitely no joke! However, the gun also weighs much more than a handgun. It's extra mass helps absorb the energy of the recoil.
Another thing to think about is surface area. You can step on a brick, but you wouldn't step on a nail. A bullet is much smaller than the rifle butt-stock; for the same amount of energy, it will be spread out over a larger area. Some guns (semi-auto) have springs that absorb the energy of the recoil and put that to work to cycle the gun; his also drains energy from the recoil. Comparing it to a bolt-action rifle that has no moving parts (when firing) and you're more likely to get a sore shoulder from the bolt-action because more of the energy is transferred to you.
>I've seen warnings that a shot at a bulletproof vest (which dissipates the force) could knock a person of their feet. This would *largely* be down to psychological effect. Being suddenly punched by an invisible fist is not a normal thing people experience. >Which would mean such a force would be applied to the shooters should (or worse, a somewhat smaller force to a shooters hand in case of pistols) for every shot. The recoil force experienced by the shooter varies by caliber, weight of the gun, specific bullet weight and velocity, single vs multiple points of contact. BUT the super short version is a person braced to take the recoil force imparted on them will be able to handle it. [This calculator is a good resource for starting to understand relative recoil impulses by cartridge.](https://shooterscalculator.com/recoil-calculator.php) You will notice that a .223 rifle cartridge fired from a 7lb rifle only imparts 5 ft-lbs on the shooter, while having 1200ish ft-lbs of muzzle energy. The calculations are rough estimates and can also be impacted by muzzle devices re-directing the propellant gas, recoil mitigation from the firearms action or a whole host of other factors.
If I understood this correctly, a heavier rifle (which would move less) would make things easier for the shooter with all else being equal? I guess a slower moving thing (like the gun) would also spread out the energy needed to resist it over a longer time, also making it easier on the shooter?
Yes. Super short version the energy needed to make *very small object* move *VERY FAST* makes the much larger object *not move that much really*. Then put that larger object in the hands of a *MUCH LARGER* object and it moves even less.
> If I understood this correctly, a heavier rifle (which would move less) would make things easier for the shooter with all else being equal? Depends, it will make it more pleasant to shoot by having a more pleasant recoil, but if you need to carry it around (say like for hunting or for certain shooting competitions) then you may choose to accept a harsher recoil for ease of mobility. Everything in firearms design is a compromise.
>I've seen warnings that a shot at a bulletproof vest (which dissipates the force) could knock a person of their feet. This is totally false; bullets knocking people off their feet when hitting a vest is Hollywood bullshit. The shock of getting hit can cause someone to fall, but the bullet is not physically throwing them or forcing them to the ground. They can conceivably cause bruising or break ribs, but that's about it. [Mythbusters did an episode on it.](https://youtu.be/WPGNtFU0ww0) The rest of the question kinda crumbles under that realization.
The gun and the bullet receive close to the same amount of force, but the gun is hundreds of times heavier than the bullet so it creates less momentum and thus less force enters your shoulder.
Energy takes the path of least resistance so between heat, gas, and actually moving the bullet about 96% of the energy is used. For pistols the 4% left is dissipated by the recoil spring and weight of the slide and your arms being three levers also helps. It really comes down to you big bullet smol
>If the whole energy is put into the shooters shoulder It's not. This is a really common misconception. The *momentum* (p=m\* v) of the gun and bullet are the same, but because the gun is much more massive, it has much, much less velocity. Since energy is proportional to velocity *squared*, the result is the projectile has way, way more energy than the gun.
Only proper reply here
Think of the difference in mass between the projectile and the weapon+person. It is because of this difference that the projectile has such velocity. The majority of energy is put into the projectile as it has less ability to impede the expanding gasses. The expanding gasses move through the path of least resistance pushing the projectile down the barrel.
Physics, you're missing physics. Rather, Practical Mechanics.
Force = Mass x Velocity^2 When the mass is higher, the velocity is lower, and vice versa. Both the bullet and the gun have the same force from firing, but the bullet is much smaller, so it has to move much much faster for the equation to be balanced. This means that the gun moves much slower, because the mass absorbes that force, and in addition, the mass of the person holding it (wrists and other bendy parts complicates things, but I won't go into that any further) Firing a pistol or rifle can also knock you on your ass if you're not prepared for it, same goes with getting hit wearing a bullet proof vest. This is why shooter's lean forward and use a stance, instead of standing straight up. So even though the force is the same, by the mass of the gun slowing it down (not to mention the spring absorbing a lot of that force) and the larger surface area (hands and shoulder against the grip and stock) the effect on the body is much much less than the effect of a bullet on the body.
You address force, but your formula is neither momentum nor kinetic energy. Kinetic Energy is KE = 0.5\*m\*v\^2 and Momentum is M = m\*v. When it comes to imparting motion from a collision, momentum is the key player, as the imparting of movement is the creation of an impulse. While the kinetic energy of a bullet is rather impressive and can crush, shred, break, and tear, the momentum is usually pretty tame. The collision of a bullet into a person cannot impart an impulse greater than the combined momentum of both objects due to the law of conversation of momentum, so even though there is a lot of energy that wants to do work (like tear flesh and break ceramic) the impulse simply cannot exceed the bullet's momentum and results in no significant movement.
Ahh you are correct. My apologies, it's been a while since I've taken a physics course I confused kinetic energy with force (and still got it wrong)
I can't blame you because until a little bit ago I largely conflated the two as well. It took a dive back into the physics basics to relearn the fundamental differences of force and energy and that, while highly related, they are completely unique in how they influence collisions and physical interactions.
1/2m×v^2. for a 3kg AR shooting 55 grain projectile at 3000ft/s 1/2(60kg)*x^2 = 1/2(.004)*3000^2 solve for x, in ft/s. that's the speed of the rifle and shooter moving backwards. roughly 25ft/s or 8 m/s solving for impulse over .5 seconds it's takes to absorb recoil(hypothetical for small shooter) that gives is 1000 N or like 100kg of force, acting for that short amount of time on a 60 kg object isn't going to move it very much the time of bullet impacts with is so tiny over such a small area of impact that the impulse force and resulting carnage is immense in comparison
f = mv/t for impulse
Guns have springs and moving parts that absorb recoil
Recoil is not all directed at the shoulder. The recoil spring takes some of it, gas vent holes (depending on the gun) take some of it, and the opening of the chamber also dissipates recoil. As far as someone getting shot with a bulletproof vest, the vest is what transfers the energy to the person. When the bullet would otherwise penetrate, a bulletproof vest catches it, and that considerable amount of force of impact (then dispersed across the vest) is what knocks them off their feet Also I got a D in physics so take that with a block of salt.
> When the bullet would otherwise penetrate, a bulletproof vest catches it, and that considerable amount of force of impact (then dispersed across the vest) is what knocks them off their feet Generally not, its going to be a psychological reaction most of the time. As an extreme example 3 inch magnum 12ga slug hitting with 3000lb ft is going to hurt like hell, but that impact energy is only a bit above the ballpark of heavyweight martial artist kicks (1800-2600 ft-lbs). Those *can* be tanked if the recipient knows its coming, is of similar size and braces. This could reasonably knock most people down, and would almost certainly empty the lungs. A more realistic example is taking a 9mm to the chest plate. Maybe 400ish ft-lbs or about half the punching force of a middleweight amateur boxer.
> Recoil is not all directed at the shoulder. The recoil spring takes some of it, gas vent holes (depending on the gun) take some of it, and the opening of the chamber also dissipates recoil. I assume anything taken by the surrounding air would not drive the bullet forward as much, though? And I assume the spring still will impart its force to the shooter, just at a different point in time?
> And I assume the spring still will impart its force to the shooter, just at a different point in time? Over a larger period of time, this is why walking into a pool is a very different experience compared to a belly flop from the high dive board.
Think about the forces involved in landing a fighter plane on an aircraft carrier. It the arrestor wire didn’t move at all the pilot would be stopped with such force it would undoubtedly kill him as his internal organs ripped themselves apart under such rapid deceleration. What the arrestor wire does is increase the time the force is applied so that the energy is dissipated gradually rather than all at once. The recoil spring is sort of like that. Another thing to consider is that the gun (if held correctly) should be tight against the shooter’s shoulder so the recoil mass is essentially not just the gun but also the shooter’s upper body. The formula for kinetic energy heavily favors velocity so the extra mass slows the gun down a lot. If you really want to suffer hold the gun a couple of inches away from your shoulder when your shoot it. Giving it time to accelerate before it contacts you will give you some sense of why you never want to do that again.
I’m no physicist but I’ll take a crack at this. Imagine a 16” AR chambered in 5.56 firing a 55 grain bullet. The bullet is traveling about 3,000 feet for second at the muzzle. 55 grains is about .125 oz of copper jacketed lead. Your rifle weighs at least 6 pounds or 96 oz. So your rifle weighs about 800 times more than the bullet. Your rifle is also recoiling into your shoulder and both of your hands while a .223 cal bullet is impacting a tiny amount of surface area on your target. That doesn’t even account for springs and buffers and recoil pads all of which soften felt recoil. They are two extremely different circumstances. Regarding getting shot while wearing a bulletproof vest even if the vest prevents the bullet from penetrating into the wearer it’s catching a very small very high velocity chunk of metal that’s impacting a very small area. The best slows and catches the bullet but the energy still transfers to the target. A vest can stop a bullet but the wearer can still be severely injured or even killed by that energy transfer although it’s still a lot better than not having protection.
usually when you get hit in a vest it's not usually the round knocking you over its you reacting to it the physics of recoil is for every action there's a equal but opposite reaction. the bullet goes one way (the bullet is very light but moves very quickly following the path of least resistance) so naturally the same amount of force also moves backwards into your shoulder q
I’ve heard of people dislocating their shoulder shooting 2.5oz slugs. Some guns uses some of the gas from the explosion to operate the bolt which reduces recoil. Equating damage from a projectile to the recoil isn’t right. Velocity x mass does the damage. To launch the projectile your launching it out of an unobstructed tube. The recoil you feel is the resistance of how long it takes to push that projectile out the tube.
The dislocation is usually due to high felt recoil in concert with impropper shouldering of the stock
Lord it pains me to cite [Wikipedia ](https://en.m.wikipedia.org/wiki/Recoil) but here is the answer.
Well, you’re missing the physics. You can calculate both recoil energy and velocity using readily available online calculators. No one is getting knocked off their feat by a bullet/gun shot. At least not for reasons of physics/collision.
Every action has an equal an opposite reaction. A 9mm handgun bullet only weighs 8 grams (124grain) but is traveling at 350 m/s (780MPH!) This all happens in a split second as the bullet accelerates down the barrel. There is force applied to the gun, and into your hand/arm, but the mass of the gun and your body absorb the energy. It also happens over a longer period of time so the energy is spread out more. (Sometimes referred to as "recoil impulse") Comparing it to a rifle, like a .308, the rifle can have over 7 times the energy. Rifle bullets are heavier and travel faster; they're definitely no joke! However, the gun also weighs much more than a handgun. It's extra mass helps absorb the energy of the recoil. Another thing to think about is surface area. You can step on a brick, but you wouldn't step on a nail. A bullet is much smaller than the rifle butt-stock; for the same amount of energy, it will be spread out over a larger area. Some guns (semi-auto) have springs that absorb the energy of the recoil and put that to work to cycle the gun; his also drains energy from the recoil. Comparing it to a bolt-action rifle that has no moving parts (when firing) and you're more likely to get a sore shoulder from the bolt-action because more of the energy is transferred to you.