Talk:Recoil

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Due to the length of this talk page, I archived much of it by creating an archive page.Greg Glover 22:34, 21 March 2007 (UTC)

Contents

[edit] Archives

Greg Glover 22:45, 21 March 2007 (UTC)

[edit] Stuff to be done

  • Tie in muzzle brakes, along with examples above of powder/bullet masses.
  • Add issues of recoil and controllability with rapid fire
  • Bore height and muzzle rise
  • Shotgun recoil absorbing stocks
  • Recoil absorbing materials (sorbothane, neoprene)

The contents of this subheading has been archived (March 07)Greg Glover 22:31, 21 March 2007 (UTC)


[edit] Rewrite proposal

Here are the topics I listed above, plus the existing article topics, in a possible outline:

  • Definition of recoil
  • Recoil vs. energy (probably change to "momentum vs. energy")
    • Recoil is the reaction, and is a function of momentum
    • Ways to quantify recoil
    • Recoil energy can be calculated if the firearm mass is known
  • Perception of recoil
    • Psychological effects
    • Controllability
    • "sharp" or "snappy" recoil vs. "soft" recoil
    • Bore axis and torque
  • Recoil in mounted guns
    • Rigid vs. soft mounts
  • Controlling recoil
    • Tie in muzzle brakes, along with examples above of powder/bullet masses.
    • Shotgun recoil absorbing stocks
    • Recoil absorbing materials (sorbothane, neoprene)
  • Myths

As for definitions and units: I think "recoil" should be defined as the phenomenon that results from conservation of momentum when a projectile is launched. Since recoil is a function of momentum, I think that if we're going to pick a unit for "recoil", it should be mass times velocity. "Free recoil" is a measure of the recoil of a particular firearm/cartridge combination. This can be, and most often is, expressed as kinetic energy, or mass times velocity squared, with velocity being the velocity the firearm would reach if hung from string and fired.

See the below argument and references for recoil being a function of energy not a phenomenon. I woul propose recoil is a concept or theory of the law of conservation of momentum. Also “free recoil”differs for “felt recoil” in that, felt recoil is subjective to the individual person and is not established science. Free recoil is equal to measured recoil energy and therefore is is established sciance The a phrase "free recoil" like "felt recoil" are both form the vernacular.Greg Glover 18:22, 5 October 2006 (UTC)

As for perception issues: I think the difference between "soft" and "sharp" recoil, for two loads with the same free recoil energy from the same firearm, has to do with acceleration. A light, fast bullet will accelerate the gun faster than a heavy, slow bullet, and this means that the sharp load will accelerate the gun to a higher percentage of the free recoil velocity before the shooter's body starts to slow it down (since people are squishy, it's going to have room to accelerate). A soft load accelerates slower, and therefore will have compressed the shooter's body before it reaches such a high velocity, and will therefore won't reach as high a percentage of the free recoil velocity. Because of this, neither momentum nor energy is sufficient to quantify a shooter's perception of recoil, but the duration of the acceleration has to factor in there as well. scot 15:00, 3 October 2006 (UTC)

I like out line. I agree that the discussion is momentum (mv) vs energy (mv2), rather than recoil vs energy. This is the same discussion (actual they were torrid arguments) Newton had with Leibniz.
Newton who new more about the universes than any body over looked the subject of kinetic energy altogether. Well that’s my conclution based on his works and writings because Leibniz wrote the first theoretical KE equation. However Newton must have known of kinetic energy because every kinetic energy equation today is based in the second law. Anyway Newton championed mv and Leibniz championed mv2.
  • Also it was Emilie du Chatelet work ca1736 that settaled the question of mv vs mv2. A major contributer to that work was Willem ‘sGraevesande. s’Graevesande stated this: The force of a body is proportional to the mass multiplied by the square of its velocity. Restated; the force of a recoiling small arm is equal to its mass times velocity squared.

Edited by self to add references and complete the thought.Greg Glover 17:40, 5 October 2006 (UTC)

Greg Glover 4 OCT 06



[edit] a very small comment on the recoil dilemma

Frankly, folks, I feel the whole argument is kind of silly. f=ma is very important here. You could also define recoil as "work". So here's the simple answer. If a firearm produces work in recoiling (my hand weighs three pounds with the gun, it moved three inches up, and gravity and my triceps brought it back), recoil can and should be expressed in terms of energy. I believe this is Chuckhawks' way of expressing recoil as well -- in joules. This allows you to do comparitive analysis of recoil, such as back-of-the-envelope estimations of "a punch in the arm" "a kick from a mule" "a bowling ball dropped on your toe" and such.

And really, the technical detail here, while relevant, is entirely silly. It's starting to look like Loop quantum gravity which has had its own set of "my physics is better than yours" wars, too.

Yawn. Sorry I can't be more... erudite. ... aa:talk 09:42, 30 October 2006 (UTC)

I completely agree with you. However it seems many folks view firearms from a prospective of quantum physics and conservation of momentum. I like many people cannot read or write in calculus. So I cannot view the physics of firearms from the prospective of quantum physics. All I know is that a bullet goes forward and I go backwards. Then I use a simple calculation that tells me what I felt while shooting. I find much of this argument the same as the one in my office, "It feels like an icebox in here. No, its to hot in here." And the thermostat reads 20c (68f) degrees.Greg Glover 23:55, 2 January 2007 (UTC)

[edit] Its Not Newtons Third Law

According to my sources (http://www.intuitor.com/moviephysics/ , under the box entitled It's Not Newtons 3rd Law, about 2/5 of the way down) the recoil has little to do with Newtons third law and it can not be used to explain why victims in real life do not fall backwards.

Therefore I think the section on recoil, like many have said does need to be rewritten, or at least written off for the moment. EvilGuru 23:14, 11 March 2007 (UTC)

Well, one of the unwritten rules of firearms is "Anything you've seen about firearms on TV or in a movie is almost certainly false". Recoil is the phenomenon experienced by the shooter, not the target, and has everything to do with action and reaction. The movement of a live target, when hit with small arms fire, has more to do with the target's response than any transfer of momentum to the target. In the case of movies, the target is generally attached to a wire that is use to pull them rapidly backwards... A metallic silhouette target, on the other hand, reacts only to the momentum of the bullet, so that is governed by the 3rd law. scot 15:22, 12 March 2007 (UTC)
Recoil vs Energy was rewriten by agreemnet (see my wiki page) and posted today. EvilGuru I second your thought. Are you ready for a "Perception of Recoil" rewrite.Greg Glover 00:11, 14 March 2007 (UTC)

[edit] Momentum vs Momentum

I think some of the authors of the “Recoil” article are confusing “Classical” momentum with Conservation of momentum.

Now, I am by no means a mathematician. But it strikes me, after reading the Momentum article that momentum differs from Conservation of momentum. My understanding of the article is that momentum fundamentally conveys velocity. The definition for momentum explicitly states, “…momentum is frame dependent”. Therefore momentum is a measurement of velocity for an object in motion. If the velocity of an object is known then it can be measured for its transitional kinetic energy. Transitional kinetic energy is also frame dependant.

If we read farther in the article, it explains that “Momentum for a system” relates force to momentum per time: F=p/t, F=mv/t, F=md/t2 then F=ma. This explanation leads me to believe that momentum per time related to kinetic energy through Newton’s second law. Therefore the head description of recoil in the recoil article of being “…about the backward momentum produce in firearms…”, is in direct contradiction to the contention that the recoil of a firearm is related to or a concept of Conservation of momentum.

What I get from the article concerning Conservation of momentum is that it is the concept of a zero sum gain. The article says that Conservation of momentum relates to Newton’s first and third laws of motion.

Again as in my previous postings, the first and third laws of motion fold into one another. However the second law stands as an independent equation with differing applications than to the first and third laws.

Therefore I can only conclude that the “recoil article” is fundamentally incorrect based on the information contained in the Wikipedia article “momentum”.Greg Glover 04:36, 22 March 2007 (UTC)

The momentum of a closed system is always constant, and generally held to be zero since the frame of reference of a closed system is generally relative to that closed system (hence that whole theory of relativity, which basically states that there is no absolute nonrotational frame of reference). However, zero sum momentum applies ONLY to closed systems. Yes, if you take a firearm out into space and fire it, the center of mass of firearm plus ejecta remains exactly the same as it would have had the firearm not been fired; however, as soon as the firearm or ejecta interact with an object outside the system, it is no longer closed. Since the general frame of reference used by the shooter is the shooter's body, firing a firearm does result in velocity being imparted to the firearm; this velocity can be expressed in many ways, including as kinetic energy OR as momentum. You CANNOT calculate recoil based on energy; if I say I have a 2000 ft. lb. cartridge, and ask you to approximate the recoil of a .3 slug firearm, you CANNOT tell me, because recoil is NOT based on energy. If I say I have a 2.68 lb-s cartridge, then you can calculate the recoil of that .3 slug firearm, by applying the principle of conservation of momentum. Recoil IS conservation of momentum, pure and simple, now matter what mathematical gyrations you go through to get there, and no matter what units you express it in. scot 13:56, 22 March 2007 (UTC)
I am sorry Scot I have no idea what you are talking about. You speak in a language that is foreign to me.
You wrote, “you CANNOT calculate recoil based on energy.” That is correct. Just as you can’t calculate the velocity of a bullet from the velocity of that bullet. Or, you can’t calculate the weight of a firearm from the weight of that firearm. Your statement is just what I have been telling you since November of last year. Recoil is a function of energy.
As you know anything thing divide by its self is equal to one. So if I figure for the recoil energy of a firearm using the recoil energy of that firearm I will derive the value of one. So, recoil energy is found by using the momentum equation to find for the velocity of the firearm. Then the found velocity of the firearm is plugged into the transitional kinetic equation to find the recoil energy of that firearm . Why? Because momentum is equal to velocity and recoil is equal to energy.
Your conservation of momentum has no place in an article explaining recoil as a measurement of energy for firearms: large or small; handheld or mounted.Greg Glover 20:18, 22 March 2007 (UTC)
OK, let me try a completely different approach, from first principles... scot 22:14, 22 March 2007 (UTC)
Well I see where we agree. Your math and my math derive the same values. Our miscommunication is due to our styles of writing and prospective of recoil.
But I finally see where we disagree. You view the backwards momentum of a firearm as an equation: mv = mv; p = p and Ep = Ek. I view the backwards momentum as a term: mv; v; and Et.
So I will now leave it up to yourself and others to rectify (if need be) this article. Thank you for the stimulating discord. I will move forward with free recoil.Greg Glover 01:12, 24 March 2007 (UTC)
Expanded thought
It also occurred to me that you view recoil from a one firearm at-a-time prospective. That is, if you view recoil from the prospective of an equation then you are comparing the “backwards momentum” of the firearm to the forward momentum of the projectile (powder charge included). Hence you only view one firearm at a time. Your ballistics program below shows this quit clearly.
I on the other hand view recoil by comparative analysis. Because I view recoil as a term, I can compare one, two, three, ect…, firearms at a time. This is what I believe the casual reader is thinking when they read about recoil as it pertains to firearms.
If you would like run these numbers in your ballistics program to check them that would be fine with me. I would be interested in what you come up with. I use 5200 f/s as a charge velocity for rifle cartridges and 32.163 as the dimensional constant (acceleration of gravity). Also my program rounds off the Momentum values.
Cartridge .458 Winchester .30 x 50BMG
Bullet 500 grains 180 grains
Muzzle Velocity 2150 f/s 6000 f/s
Powder Charge 74 Grains 235 grains
Firearm weight 12 lb 12lb
My results:
Recoil 56.3 ft • lbf 140.1 ft • lbf
(Recoil 30.8 ft • lbf 31.1 ft • lbf With no powder charge velocity computed)
Muzzle energy 5133 ft • lbf 14389 ft • lbf
Bullet Momentum 154 154
Greg Glover 05:48, 27 March 2007 (UTC)
Cartridge .458 Winchester .30 x .577 Tyrannosaur
Bullet 500 grains 180 grains
Muzzle Velocity 2150 f/s 4064 f/s
Powder Charge 74 Grains 140 grains
Firearm weight 12 lb 12lb
My results:
Recoil 56.3 ft • lbf 56.3 ft • lbf Powder charge velocity computed
Muzzle energy 5133 ft • lbf 6601 ft • lbf
Total Momentum 209 209
Greg Glover 14:16, 27 March 2007 (UTC)

[edit] Internal ballistics simulation and recoil

Newton's laws of motion:

  1. An object in motion will remain in motion unless acted upon by another force.
  2. Force equals mass times acceleration.
  3. For every action there is an equal but opposite reaction.

Let's start with JUST law 2: F = m * a

A closed form solution to a ballistics problem would require more calculus than I'm comfortable with, so let's do things the old fashioned, pre-calculus, iterative way. It works better anyway, since computers can do the huge number of calculations for us, and doing iteratively means we don't have to worry if our functions can't be expressed in nice neat forms.

Lets start with a good, solid example; a 2.5 lb. .45 ACP with a 230 grain bullet, a 5 inch barrel, a chamber volume .45 inches in diameter and .5 inches long, and 20,000 psi of chamber pressure. We'll ignore bore friction for right now, since it's a constant and negligable compared to the resistance provided by the inertia of the bullet, and also ignore powder burn rate (we assume it's all burned by the time the bullet has moved significantly--this will give us higher than realistic velocities) and any adiabatic cooling and heat loss. All of these things are secondary to the main concern, which is calculating acceleration--the pressure simulation just gives us a rough approximation of a chamber pressure curve, and any f(t) would work just as well, but this at least keeps us working with real numbers.

Here's the source code for the simulation, written in BASIC:

' constants
pi = 3.14       ' ratio of circumference to diameter
g = 32.2        ' gravity in feet per second per second

' units in feet, seconds, and slugs
'  EXCEPT bore and pressure, which are in pounds and inches
distB = .5 / 12              ' distance bullet has travelled down barrel
distG = 0                    ' distance gun has recoiled
length = 5 / 12              ' length of barrel
diameter = .45               ' bore diameter
pressure = 20000             ' chamber pressure (psi)
massB = 230 / 7000 / g       ' mass of bullet (230 grains)
massG = 2.5 / g              ' mass of gun (2.5 pounds mass)
velG = 0                     ' velocity of gun
velB = 0                     ' velocity of bullet
time = 0                     ' elapsed time of simulation     

' simulation time step, seconds
dt = .00001
                       
' calculate inital chamber volume, cubic inches
vol = distB * pi * (diameter / 2) * (diameter / 2)

CLS

WHILE distB + distG < length
       ' calculate volume of gas
       volNew = (distB + distG) * pi * (diameter / 2) * (diameter / 2)
       
       ' calculate new pressure based on expansion
       p = pressure * vol / volNew

       ' calculate force based on bore diameter and pressure
       force = p * pi * (diameter / 2) * (diameter / 2)

       ' calculate acceleration, f=ma -> a = f/m
       accelB = force / massB
       accelG = force / massG

       ' calculate velocities
       velB = velB + accelB * dt
       velG = velG + accelG * dt

       ' calculate travels
       distB = distB + velB * dt
       distG = distG + velG * dt

       time = time + dt
WEND
                                       
PRINT "Bullet has exited at time "; time; "s"
PRINT "Residual pressure         "; p; "psi"
PRINT "Bullet velocity           "; velB; "fps"
PRINT "Gun velocity              "; velG; "fps"
PRINT "Bullet energy             "; velB * velB * massB / 2; "ft-lbs"
PRINT "Gun energy                "; velG * velG * massG / 2; "ft-lbs"
PRINT "Bullet momentum           "; velB * massB; "lb-s"
PRINT "Gun momentum              "; velG * massG; "lb-s"
PRINT "Bullet travel             "; distB; "feet"
PRINT "Gun travel                "; distG; "feet"

And here is the output:

Bullet has exited at time  6.900001E-04 s
Residual pressure          2009.819 psi
Bullet velocity            769.0192 fps
Gun velocity               10.10711 fps 
Bullet energy              301.7299 ft-lbs
Gun energy                 3.965591 ft-lbs
Bullet momentum            .7847134 lb-s
Gun momentum               .7847134 lb-s
Bullet travel              .4174829 feet
Gun travel                 4.939299E-03 feet

The gun is 76 times heavier than the bullet, and the velocities reflect that ratio, as do the energies. Note that the momentums, defined as mass times velocity, match exactly. I am ignoring powder mass, but as it's only 5 grains and will be accelerated by only 2000 psi for a very short span, that's not a lot compared to the 230 grain bullet at 20000 psi. scot 22:14, 22 March 2007 (UTC)


[edit] Newtons laws

The backward momentum is equal to the mass of the gun times its reverse velocity. This backward momentum
is equal to the sums of the two forward momentums by the law of conservation of momentum and is due to 
and equal to the projectile's mass times its velocity added to the mass of the escaping gases, burnt 
propellant, unburnt propellant, and other gases, times their respective velocities.

newton third law governs recoil, conservation of momentum is relevant at the point of impact has little to do with recoil

What? So the interaction between bullet and target is subject to the laws of physics, but the interaction between firearm and bullet is not? ALL particle interactions— elastic and inelastic—are subject to conservation of energy AND conservation of momentum. Newton's third law describes the effects of conservation of momentum. In the case of recoil, the third law requires that the momentum of the ejecta (the action) be balanced by the momentum of the firearm (the reaction). Even rotational inertia must balance out, so the firearm twists a tiny bit in the direction opposite the bullet, though this force is tiny enough that the shooter is generally unaware of it. scot 22:37, 26 March 2007 (UTC)
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