I have a question for everyone, and I hope you all can help.

I was told by a coworker the other day that chamber pressure has a larger effect on felt recoil than recoil energy. Her, reasoning is that, the pressure of the cartridge dictates the recoil force of that cartridge, which in turn, dictates how quickly the recoil energy is delivered to the shooter.

She further stated, that the shooter's perception of the severity of recoil, was directly related to the rate at which the recoil energy was absorbed by the shooter. So the higher the recoil force the more severe the recoil is perceived to be by the shooter.

The entire discussion seems to make sense to me, but I have never heard of anyone talking about recoil force before. What do you all think? Is she full of it?

Thanks,
Lucs

I think that increased pressure will increase the jet effect of recoil.

Higher pressure results in a quicker acceleration of the bullet, which results in an opposite reaction by the firearm.

Lucs,

I think your coworker knows what she is talking about. Recoil is the force of the rifle coming back at you in reaction to all the forces involved in firing a bullet.

Pressure is force per unit area, and the force acting to the rear is a component of recoil. A major component is the reactive force of the bullet being accelerated down the bore. Another component is the reaction torque from the rifling spinning the bullet; while as 500grains mentioned above there is a rocket effect from the gases moving down the bore.

The shape of the pressure curve is also going to strongly affect the felt recoil, along with other factors like the stock configuration, etc.

jim dodd

I'll take the opposite point of view and assert that pressure _by itself_ has nothing to do with recoil. The only factors that contribute to recoil are the mass and velocity of ejecta (bullet and powder gasses) and the mass of the rifle or gun. Consider, for instance, a .30-06 loaded with 180 grain bullets at 2700 fps. You could achieve this level of performance with a fast powder like 3031 (or even 4198 if your rifle would take it!) or with a case full of 4831. The more powder used, the higher the recoil. And yes, you _can_ feel the difference in the above loads.

I have read and believe that the burn time involved in building up pressure to push out the projectile, greatly effects velocity, accuracy, and felt recoil. There have been some tests done where using fast and heavy charges actually strip some of the outer layer away from the bullet(s). Inturn, this caused the projectile not to be spun at the correct turn rate for best flight stabilization IE: poor accuracy. Also, gas pressure blow by was also present which actually caused poor velocities when chamber pressures were extremly high.

So yes, internal chamber pressure does have an effect on felt recoil. Try it, hand load with a slow burning powder which normally requires a more heavier of charge, and then load some rounds W/some fast burning powder with the same weight of bullet (using loading data).

Try to find powders that W/safe loadings provide the same chamber pressure, but burn opposite IE: one very slow, and the other very fast (for the given caliber in question).

Chances are you'll find the slower burn powder charged load will give you heavier recoil (more pushy) but not as fast of a recoil velocity... IE: snappy feeling. The faster burning powder will give you a snap, but not near as much felt recoil (push).....

Hope this helps,
Dennis
Happy Sporting

Thanks for the interesting comments guys. Calculating the recoil energy and velocity are straight forward. How do you calculate the recoil force?

Paul H, she is not a shooter. She is holds a Masters of Science in Physics. She overheard me talking to a few other coworkers about the recoil of my 500 A Square. This evidently interested her, and she joined in the discussion. After I had filled her in on how a gun worked she provided her expert opinion on the mechanics of recoil.

Her expert opinion surprised me since she maintained it was the recoil force not recoil energy that was important. I had never heard anyone say that before until she had and now a few others who substantiated her claims on this thread.

Thanks for all the comments.

Lucs

416 rigy, 416 rem... rigby, in same weight gun, kicks more for same vel and bullet. it's buring 20 more grains of powder, even though the pressure is lower. and, a 416 taylor, at 2250, feels like a 22 after either.
jeffe

As it has already correctly been pointed out, the pressure of a burning propellant charge has nothing to do with recoil, felt or real. It never has and it never will.

Recoil = momentum = mass X velocity. Since there is no variable for pressure in that equation, pressure has no effect on recoil, regardless of how "intuitively obvious" it may seem. Whether you use the mass and velocity of the rifle or the mass and velocity of the ejecta (bullet + burning gas) it matters not, since the law of conservation of momentum states that both products WILL be equal. These are physical laws whcih have no exceptions.

The WORK done by the recoil on you, IS dependent on the time it takes for the ejecta (and thus the rifle) to accelerate to its final velocity. That is because work is force per unit time. The work of the recoil is only one component of felt recoil, as felt recoil is a puerly subjective measurement which includes not only the time element, but also stock fit, recoil pad hardness, upper body composition, facial features, etc., etc., etc.

I don't have a masters in physics, just a bachelor's in marine engineering. But all you need to understand this is a basic college level text book on physics or engineering mechanics.

As to whether the lady mentioned above is a shooter or not, that's irrelevant. This isn't a marksmanship question, but a physics question. In fact, it's better that she's not a shooter. That way she doesn't bring all the preconceived "common sense" notions that many shooters bring to the table.

Just let her shoot your 500A2, and she'll have a much better appreciation for felt recoil.

The biggest problem with calculating recoil is the mass and velocity of the gases are ignored by most calculations, despite the fact they have a signifigant effect! This is clarified by two points, you can have two guns with the same stock, same weight, but one has a barrel 4" longer. The gun with the longer stock has increased velocity, but the recoil will be identicle between the two. The other example is the muzzlebrake, which would not work if the escaping gasses have no componet to recoil.

[ 01-16-2003, 01:09: Message edited by: Paul H ]

Paul, I would love to get her to shoot the 500 A Square. The problem is no one will shoot it! Everyone seems to be scared of the recoil.

Lucs

Hmmm, maybe they do have an understanding of what fealt recoil is

Pressure has a lot to do with recoil. Without pressure, there is no recoil at all. Velocity has nothing to do with recoil. Change of velocity (acceleration) has everything to do with recoil.

Read your post. You just contradicted yourself. I'm quite well versed in physics and engineering.

500 A2,
Simply put, anything that increases shove to the front end, does the same to the rear end. A 150 grain bullet from a .30-06 driven by 50 grains of a powder will result in less recoil that exactly the same set up using 55 grains of the same powder. However, you're talking apples and peaches when you talk about recoil energy and felt recoil. The Winchester M-94 in .30-30 has less recoil energy than a well stocked .30-06. But gives me more felt recoil. A poor fitting stock can change a sweetheart rifle into a real pain. In the example of the M-94, the drop at the heel of the stock actually causes more muzzle flip than a stock with little or no drop at the heel of the stock. For someone my size, the short trigger pull of the M-1 Garand, took some getting use to. The weight of a rifle makes a big difference in felt recoil. Just my nickles worth. Good luck.

You guys may be interested in this - turns out that maybe the leading cause of recoil is the rifling because of the instantaneous spin (approx 3000 rpm) applied to the bullet and the counteracting torgue - which is distributed backwards. A smooth bore elephant gun firing a 1000 gr bullet at 2400 fps will seem gentle compared to a 600 Nitro Express - it is also why a modern smooth bore tank does not reguire a muzzle break. I'd like to take credit for this wisdom but I just read it in Jeff Cooper's book "The Art of The Rifle".

Guys, I almost forgot to add another internal pressure factor involved in recoil dealing W/pressure, "the jet effect". Once the projectile leaves the bore seal very high pressure escaping gases continue to excape from the barrel IE; muzzle. THE greater release of pressure, the more jet effect, and inturn the more felt recoil. This escaping of high pressure gas from one end mimicks that of a jet, in that it pushes the source away from the opposite of where the gas is escaping from. The jet effect has a great deal which influences felt recoil.......... That's why we have muzzle brakes to redirection the "Jet Effect". In the BMG 50's, the gasses are even redirected to pull the rifle forward GREATLY aiding in felt recoil. Some say that full power 50 BMG loads feel like 243 win loads when those type of brakes are used.

The are many factors that can effect felt recoil, why are we trying to say that one does it all, or one factor IE: internal pressure, doesn't have any effect at all, when in fact they do. The varying factors vary depending on how different they are used. There are many factors in determining felt recoil ?

Dennis

>The gas velocity inside the barrel is the same as the bullet. <

Wrong again, k. Only the gas right at the base of the bullet has the same velocity as the bullet. The gas at the base of the cartridge case has zero velocity, with respect to the gun.

I have to agree T_Bob's right on this one. In the time between powder igintion and bullet exit, the center of mass of the powder charge only moves from slightly behind the bullet (initial) to half way between the rear of the chamber and the muzzle, volume wise(assuming complete combustion of the powder in the barrel). Thus, the muzzle velocity of the powder charge is just barely over half of the muzzle velocity of the bullet(slightly longer distance in the same time) PRIOR to bullet exit. As soon as the bullet "unplugs" the bore, barrel pressure returns to 1 atmosphere extremely quickly. High speedphotos show this clearly; the powder gases pass the bullet immediately upon exit. For what it's worth, A2 assigns an average gas velocity of about 5200 ft/sec for its calculations, other references differ. Clearly this will vary slgihtly with the chamber/barrel pressure upon bullet exit(not necessarily peak pressure; final pressure will vary with powder type/weight, barrel length, and bullet weight, among other factors),and recoil acceleration and therefore FELT recoil will vary with the pressure curve of a given load.

A load that uses 50gns of powder to propel a 55gn bullet 3500fps in a given case with an 18" barrel will procuce slightly more recoil than a load that uses 50gns of the same powder to propel a 55gn bullet 3500fps in an 20" barrel, assuming the pressue peak occurs in less than 18" and similar pressure curves.

This is because in order to achieve similar bullet velocities in the shorter barrel, average (not peak) pressures must necessarily be higher.

Given 2 loads that uses the same bullet weight, powder charge, and powder type and that produce the same muzzle velocity (and therefore muzzle energy), pressures may vary sgnificantly due to chamber size, bore diameter, barrel length (thus expansion ratio), etc.

Just my 2.5 cents. -Bob

As it appears I have 3 or 4 very well versed individuals here, I would like to run my rather simplistic rationale by you for correction, affirmation or otherwise, with the hope that more readers might come away with a better grasp of the subject matter.

Let's, for example say I've got this SAKO .270 with 24" barrel. I've got two loads, both giving 3,250+ fps with the same components except for powders. Both give indistinguishable pressure indications and case expansion micrometer readings. One load uses IMR-4350 & the other IMR-4831, with two (2) additional grains of powder.

The felt recoil with IMR-4350 is noticibly sharper, faster or whatever adjective you care to apply. Despite a slightly heavier charge weight, the slower burning IMR-4831 is the more pleasant shooting load. Long ago, I got into the habit of using the term "burn-duration", in describing why this is so. Given enough barrel, many overbore chamberings may offer more desirable recoil characteristics through use of the slower burning powders.

A lot of you seem to be able to tell slight differences in recoil. I've been shooting for over 50 years, but I don't seem to be able to do that.

Bob,
Not so much the differences in the level of recoil but more the "type". At the other end of the expansion ratios, I sometimes go to faster powders, to reduce the overall charge weight, as in my .505, for example.

Yes, ksduckhunter and thank you. . Guess I can stick with my "duration" term, eh?

I suppose the math is also there to discern about where the advantages of longer pressure curves give way to the advantages of the reduced charge-weights of faster powders, as we move up in expansion ratio, in regard to the lessening perceived recoil. I don't expect an answer to that one!

[ 01-18-2003, 08:05: Message edited by: Nickudu ]

Work is force applied over a distance. Has nothing to do with itme. Power is the rate of doing work. That's when tilme come in.

Boy these conversations are interesting.

Paul H: Your hypo about the two guns with different length barrels is confusing. You wrote, " The gun with the longer stock . . .", and I believe you stated the stocks were equal. I think you meant barrels. However, you data is incomplete regarding the bullet/powder conditions. If the bullet/charge weight was the same in both guns, the longer barrel will give greater velocity and more recoil. If the charge varied to achieve the same velocity from both guns, the charge would be lighter in the longer barreled gun; however, your hypo ignores the weight of the added barrel which will have more effect on the result than the difference in charge. Steel weighs more than powder. If the longer barrel gun had the same overall weight, then the rifle with the greatest bullet + charge weight would have the greatest recoil assuming equal velocities.

KS: I don't think you are correct about "jet effect." Your basic equation works until the bullet leaves the barrel. Up until that time you are dealing with the reaction to the bullet weight and the mass of the gas. However, once it leaves, the velocity of the gases increases and you a rearward reaction to the powder/gas mass at a speed considerably greater than the bullet. Because energy is mass x velocity squared, this is considerable. Upon departing the barrel, there is no more rearward push by the bullet. The total rearward force (recoil) is a combination of the two reactions, first bullet then jet. Ku-dude

/

"The basic principle of the The Kolbe P-Max model CP-1 is simple. The more the rifle kicks, the higher the chamber pressure! "

Check out the Kolbe P-Max:

http://www.border-barrels.com/

jim dodd

Yes. Pressure does affect recoil. So I guess the real question is: HOW does pressure affect recoil? Well, pressure affects recoil in a couple of ways actually. But first, we have to take a look at just exactly what causes recoil.

Recoil is about momentum. And momentum is conserved (thanks Issac...for showing us the light). Gun recoil results from the conservation of total momentum of the bullet-gun system. That is, the backward recoil gun momentum balances the forward bullet/gas momentum to maintain zero total momentum. And momentum is the result of mass x velocity. Now, there are two basic things to take into account when calculating momentum. That is the mass and velocity of the bullet as it moves up the barrel, and also the mass and velocity of the burnt powder(gas) as it exits the muzzle. They are actually two separate (though not totally independant) events. The first source of momentum is caused by the bullet moving up the barrel. And while the momentum created by the bullet is noticable, if you do the math (which I am way too lazy to fool with right now), you will see that most of the momentum (and therefore recoil) is actually generated by the second event, which is the gas exiting the barrel. Muzzle blast, if you will. Typically, it only takes around 25 miliseconds for the bullet to exit the muzzle of a rifle, and because of the very short time span, we perceive both of these causes of recoil as one event. The combination of these two events will determine the TOTAL momentum of the bullet/gas. It is this total momentum (along with the mass of the rifle) that determines the recoil velocity of the rifle.

Here comes the pressure.

Yes, momentum = mass x velocity (thanks again, Issac). But this equation is only a way to calculate the momentum. It does not explain where the velocity comes from. The bullet did not magically go from rest to a velocity of 2800FPS. It was accelerated up to speed by SOME FORCE. And that force is the direct result of the tremendous pressure generated by the burning powder as it is converted into a gas. By definition, pressure = force/area. And since the area of the base of the bullet is constant, then an increase in pressure means there is an increased force on the base of the bullet. And the increased force on the bullet (often) leads to a greater muzzle velocity, and a greater muzzle velocity means an increase in momentum. But wait! It's not that simple. Because, as the bullet moves up the barrel, the TOTAL area that is under pressure increases. And that, in turn, causes the pressure to drop. So it also depends on WHEN the peak pressure is achieved.... which not only affects the average pressure, but also the actual pressure at the time the bullet exits the barrel. Has the bullet moved an inch or so (typical) up the barrel when the pressure is at it's peak, or has it only moved a couple of milimeters? Your guess is as good as mine. It will vary with the burn rate of the powder, and several other factors. But the point is, that the velocity of the bullet is ultimately generated by the pressure created by the burning powder. So that is ONE way that pressure affects the momentum, and thus recoil. The SECOND way that pressure affects momentum of course, is by determning the amount of "muzzle blast". The higher the pressure, the faster the gas exits the barrel. Once you take the stopper (bullet) out of the tube, the gas is no longer restricted, and it REALLY exits the barrel. And the faster the gas exits the barrel, the more the momentum is increased (again....mass x velocity). Now, this "muzzle blast" does not occur at the time the pressure peaks, but rather at the time the bullet actually exits the barrel. Remember, the pressure drops as the bullet travels up the barrel. It is also interesting to note that the momentum generated by the bullet occurs over that 25 milisecond time span, but the momentum generated by the "muzzle blast" occurs almost instantaneously as the pressure drops to zero, when the bullet exits the barrel.

So does increasing the pressure increase the recoil? The answer is a definate maybe! Read on.

If we are talking about increasing the pressure by increasing the amount of the SAME TYPE OF POWDER in the SAME gun, with the SAME bullet, and the SAME case, then YES, increasing the pressure does result in increased momentum, and thus recoil. The bullet will have a higher velocity, there is an increased mass of powder being burned, and the greater pressure will result in a higher relative velocity of the gas exiting the barrel. Of course there are some limits here. At some point, the pressure begins to get VERY high, with little velocity gain to show for it. As an extreme example: If you pack a 300 Winchester Magnum case with Bullseye powder, the gun would likely blow up long before the bullet ever exits the barrel. So in this case, you WOULD feel something (like the metal parts hitting your face), but you wouldn't really experience much recoil, even though the pressure has been greatly increased. BUT, if you change ANYTHING other than the AMOUNT of powder, then all bets are off. Since different powders burn at different rates, you may or may not get an increase in velocity of the bullet. You would also, most likely, change the total mass (number of grains) of the powder when you change types of powder. Of course going to a different weight (mass) bullet would also upset the apple cart. And who the hell knows the ACTUAL velocity of the gas exiting the barrel? All of these things COULD have a negative affect on the momentum generated, even though the peak pressure might be increased. It is also not accurate to draw any conclusions about increasing pressure when comparing two different size and shape cases, loaded with different powders, from two different calibers. In short, it is very difficult to positively say what will happen to the recoil if you increase the peak pressure by changing the various components. Sometimes you just have to take a WAG (wild ass guess).

So we once again ask the question: Does increasing the pressure result in an increased recoil? And the answer is still.... MAYBE. It just depends on the exact circumstances under which the pressure was increased. Each situation is unique.

To sum it up, pressure has an affect on both the velocity of the bullet, and the velocity of the gas as they exit the barrel. And since each of these velocities has an affect on the momentum, and because momentum is conserved, then it is easy to see that pressure does have an affect on recoil.

In reality, the BEST way to determine recoil, is simply to measure it.

Now. So I don't get flamed too badly...I'm out of here!
Good shooting.

Billy Buck got it right; it is all about acceleration.

Welcome to the forum Billy Buck. You should stick around.

All factors being equal, pressure will no doubt affect recoil but I won't say that pressure determines recoil. A .220 Swift operates at a much higher pressure than, say a 9,3x62 and their recoil is quite "different". Just try and shoot both side by side and it will convince you. I believe that bullet and powder mass x velocity are the main factors.

There are two issues here.

Billy Buck states:

"It is also not accurate to draw any conclusions about increasing pressure when comparing two different size and shape cases, loaded with different powders, from two different calibers."

This is in line with our experience that when the same rifle is compared with different loads, a ballistic pendulum shows less recoil if muzzle pressure is lowered. This is typical with faster burning powder.

With larger calibers the volume of gas expelled from the muzzle is much larger and this will contribute to felt recoil making comparisons between calibers very complex.

In both cases recoil as measured on a ballistic pendulum can be manipulated more easily by changing pressure than by changing bullet weight.

Thanks, everyone for the excellent information. As I had initially stated, my coworker's statements made a great deal of sense to me. What really impressed me about her was the fact that she said all this with a minimal comprehension of firearms and cartridges.

KSD, if you do not mind my asking, what is a marine engineer? I have not heard of this discipline before.

Lucs