Recoil/Knockdown?

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Valdez

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I was having an argument recently with a friend on the difference between gun recoil and the knockdown power of a handgun round, say one that impacts a hard trauma plate on a bullet proof vest.

He convinced me of one thing. The recoil of the gun won't necessarily be equal to the force of the round hitting the plate because a round is a form of shaped charge. The primer launches the propellant out the barrel with the bullet and burns over time.

So here's the question. How much of a difference does this shaped charge effect make? Or in other words is the felt recoil force much less than the impact force?

I may be poorly stating this question but I'd like some insight. Thanks in advance.
 
Valdez,

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>the knockdown power of a handgun round[/quote]

Sorry but there is no such animnal. The term "Knockdown" infers that the force of a bullet fired from a handgun has the power to knock a man down and it simple does not.

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John - NRA - Lifer
 
I believe that the recoil force is equal to the force that is imparted to the bullet to get it to leave the barrel. It's just that the mass of the weapon and the bullet are so unequal that the weapon moves a lot slower compared to the projectile.

At the target, the power imparted to the target is a function of caliber, bullet weight, and construction.

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45 ACP: Give 'em a new navel!
 
For every action there is an EQUAL and opposite reaciton. Hey it sounds good? I think the recoil is same as energy used to propell the bullet just that it is dispersed over much larger area (grip, stock) and gun weight is such that it appears to recoil over a longer period of time (compared to how long it takes for bullet to leave). Dont know if this is all bs, its just how I figured it would workout.
 
Sorry if I posted this thread in the wrong place though it is not(!) primarily about the "knockdown" power of a gun, it is a question of the physics of any rifled firearm.

One, I am familiar with Newton's laws but what is occuring in a gun is slightly more complicated in some respects.

Why? Well, if a round acts as a shaped charge, the powder burns over time. Further, the explosion in the back of the barrel propels the rest of the powder forward in the barrel. So the fuel(powder) is mostly accelerated by a shockwave as it is ignited.
This means that recoil takes place over time.

My friend, an ex-military type who has experience with shaped charges claims that a properly shaped charge can literally blow a tank over while causing very little damage to say a Yugo sitting next to the tank, behind the charge. Some damage of course will be incurred but he claims he has seen these effects.

I still claim that since the charge largely relies on the barrel to contain and direct it, and that the rifling is in contact with the bullet, most all of the recoil will be transfered into the weapon. He simply denies this to be true.

Is anyone here an expert on the physics of firearms?
 
Knockdown power is a MYTH!! On one of my dad's law enforcement training videos I watched a man with a bullet proof vest, standing on one leg get shot with a 30-06. THe man did nothing more than sway back a little. This was done about 2 feet from the end of the barrel. Kids to try this at home get a big sandbag filled with 200lbs of sand. Set the bag on a post, table, anywere it could fall off if knockdown power did exist. Shoot the bag with any caliber desireed. The bag will not move.


By the way, while I am not anywhere close to an expert on any of the subject matter it is my experence that an explosive shape charge is used to punch a hole in an object. Tank, dirt, ect. This is due to the Monroe? effect that concentrates the blast in a very limited direction. This generally (depending on type of explosive) has a cutting effect, not a pushing effect. Having made several field expiedent shape charges and placed them on M-60 tanks I foung that it generally made neat little holes in the tank, not moved the tank in any sort of way. Same thing in the dirt. True objects to the left and right do not have the blast pionted at them. How this has anything to do with the knockdown power of a firearm I have no idea, just my $.02 worth :)

Later
DAren
 
Valdez, you and/or your friend are incorrectly using the term, "shaped charge." a shaped charge is used in anti-armor weapons and other serious demolition activities. the general idea is that the shape of the explosive charge creates beneficial focus of the shock waves with increased destructive effect.

however, recoil momentum will be higher than the momentum at downrange impact, due to the ejecta (propellant gas and unburned powder). the big difference is that the gun's recoil force is spread over several square inches of hand, plus the impulse is spread over time. the bullet strikes a very localized area, and is a very sharp impulse.

"felt recoil" is a nebulous term; do you mean the total impulse (the integral of force over time), or the maximum instantaneous recoil force?

and the other posters are correct; there is no "knockdown effect" from handheld firearms. any time a shootee falls backwards, it is due either to central nervous system disruption, or being poorly balanced to begin with. but forget about "TV physics," all those guys flying backwards is just BS.
 
First there is no explosion, smokeless powder is a propellant not an explosive, but both are energetic materials as are pyrotechnics.
The difference between explosives and propellants is the rate at which the reaction proceeds.In explosives, a fast reaction produces a very high pressure shock in the surrounding medium. This shock is capable of shattering objects. In propellants, a slower reaction produces lower pressure over a longer period of time. This lower, sustained pressure is used to propel objects.

As to knock down power one of my tests was laying a car tire on its side on top of a table, I shot a 600 grain brenneke slug at it and it went through both sides and slide tire right off table. That is probably as close to knock down power as you will get without a true explosive blast wave. This is another reason it appears that large diameter and heavy projectiles hit harder that small fast moving. Usually the small fast loose their energy fast on the surface where large slow will keep pressing on (known for penetration and momentum) as most large african rifles will. That 06 on the vest spread it's energy rapidly over a very large area of the vest and then disipated very quick, take same bullet in your hand and presss aginst his chest and over he will fall.
A funny example would be to launch a 25 pound watermellon out with the same kinetic energy as that 06 and the guy will be on his ass. As he probably would be if hit by a hi pressure 4 ga slug that weights about 8 oz. My point being eventually you will end up with a small cannon ball and the guy will go down no matter what vest he is wearing. As slow (relative) heavy objects have more knock down than fast light.
 
Thanks for the reply.

I am convinced that Newton's laws can be applied in a fairly straightforward manner in the case of rifled firearms.

By the way, my friend might have been speaking in analogies. He was a tanker in the gulf involved in punching through minefields quickly. I realize that shaped charges are used to punch through armor, as in armor piercing rounds. I'm not sure I completely understand the physics beyond having the impression that the shock wave moving through the charge actually compresses and accelerates the explosive material to some sort of focal point.

I guess gunpowder is classified as a low-explosive, meaning that it actually burns rather than the extremely rapid phase change in high-explosives.

I think I'll make a bet with this guy.
 
By the way, Ivanhoe, I think that I am more interested in the "total impulse" or the integral of the forces over time.

Dang, my Newtonian mechanics are rusty. That's what five years of non-use will do.
 
Hi Valdez,

Lots of folks have tried to arrive at various formula for projectile energy transfer, but the variables are really numerous. The projectile as well as the target incur most of the problems. Simply think of the differences between a frangible bullet and a homogenous one. How frangible/how homogenous?

Not sure what your buddy did in the military, but I think he's getting confused between a tamped charge and a shaped one. The shaped charge burns a small hole through the target, while a tamped charge directs it's force in a linear manner due to the effects of "tamping". Think of a firecracker buried under a sandbag (tamped) versus a primer that directs it's energy into a cartridge.

Hope this helps,

Giz
 
Anti-tank shaped charges use a bit diffirent
technology to penetrate the armour. Usually
internal taper of the charge is coved with
a layer of some metal, often copper based
alloy. When charge goes off, this thin metal
skin is "forged" into some kind of relatively dense projectile, which is also heated to God knows what temperature, then driven forward awfully fast (close to speed of explosive detonation) and only then makes
or, say, burns a hole in a poor tank.

Gosh, I hate myself for being so cool...
 
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