"Trajectories" Topic

Dear All,

Not to bring up bad memories, but I found this interesting part of The Artillerist's Manual by John Gibbon first published in 1860 and updated in 1863. Gibbon was a battery commander in the Civil War, and a Regular Army captain. He was also a brigadier general of volunteers, and commanded the Iron Brigade as well as a division of Hancock's II Corps later in the war. He saw combat as both an artilleryman and an infantryman.

Prior to that he had seen combat in the Mexican War and Seminole War as an artillery officer in the 4th US Artillery. He was also an artillery instructor for five years at West Point. His credentials as an artilleryman and soldier are impeccable.

The following excerpt has to do with the trajectory of the artillery round after it leaves the gun tube:

'The ball starts along the axis, and but for its weight, would follow that line more or less closely; but as soon as it leaves the bore, its weight depresses it, and keeps it always below the line of fire…In vacuo, the trajectory would be a parabola; but in the air it is modified, and becomes less like that curve as the weight and velocity of the ball increases.' page 206.

Therefore, the round does not rise above the line of fire, as I had previously posted and explained, but starts to fall below the line of fire as soon as the round leaves the gun tube.

Even though this is an 1860 manual, the basic principles of gunnery have not changed since 1789, nor have they still today.

Sincerely,
Kevin

Except that you no longer fire ball?
So that you would not seek to increase the chance to hit a soft target by skipping the round along the ground?

The ball could theoretically rise above the line of the bore slightly by receiving a spin perpendicular to the line of flight by a slightly out of true barrel or by accident of windage. A tennis backspin is achieved by slicing the ball from below – with a barrel it could occur by the ball striking or rolling along the top of the barrel on exit imparting a spin causing a relative low pressure at the top of the ball and so a slight rise.

I recall artillerymen being concerned about barrel sag if the tube overheated, depending on how the barrel sagged this could lead to the ball taking on a rather more eccentric flightpath similar to the one documented at the time for muskets where the ball behaves just like a baseball pitcher sometimes uses swinging away before cutting back in across the direct line of sight.

As for what variations in the density and regularity of the ball could do for its flight characteristics my math gives out.

Except that you no longer fire ball?
So that you would not seek to increase the chance to hit a soft target by skipping the round along the ground?

The ball could theoretically rise above the line of the bore slightly by receiving a spin perpendicular to the line of flight by a slightly out of true barrel or by accident of windage. A tennis backspin is achieved by slicing the ball from below – with a barrel it could occur by the ball striking or rolling along the top of the barrel on exit imparting a spin causing a relative low pressure at the top of the ball and so a slight rise.

I recall artillerymen being concerned about barrel sag if the tube overheated, depending on how the barrel sagged this could lead to the ball taking on a rather more eccentric flightpath similar to the one documented at the time for muskets where the ball behaves just like a baseball pitcher sometimes uses swinging away before cutting back across the direct line of sight.

As for what variations in the density and regularity of the ball could do for its flight characteristics my math gives out.

One of the very early artillery books comments on the difference in thickness of the breech and barrel so that aligning the top of the barrel with the ground would actually have the bore pointing upwards. Something that could give the impression of the ball 'rising' out of the barrel.

Ball was very rarely fired in the ACW, either. The projectile of choice was spherical case (aka shrapnel), followed by shell. Case (aka cannister) was used at close range. Ball was used only when 1) serious penetration was needed or 2) everything else in the ammo chest was gone.

It has nothing to do with the round but basic gunnery. Note that shells were now being fired from Civil War field pieces and not just howitzers. And all of the rounds were no longer 'round.'

I don't have a problem with the impression of a round 'rising.' That isn't the problem. The issue was that the round does rise, no matter what the elevation of the gun tube, even at zero degress, which isn't true. The round will 'rise' if the tube is above zero degrees, but it either stays on the line of fire or drops. The round does not rise above the line of fire after leaving the gun tube.

Sincerely,
Kevin

I found this quite interesting :

link

The following is from "Arms and Equipment of the Civil War" by Jack Coggins and concerns ammunition for smoothbore artillery (most commonly 12-pdr gun-howitzers, but also 6-pdr guns): "Solid shot was used for battering, and against masses of troops. It was more accurate than shell or spherical case, and ranged farther…. Shell was used against buildings, earthworks, and troops under cover. Bursting charges were so small in field artillery ammunition (a 12-pounder shell contained only one-half pound of powder) that their effect was often more moral than physical. Time fuzes were used, ignited by the flash of the gun's discharge. Spherical case (shrapnel) was used against bodies of troops, usually at ranges from 500 to 1500 yards. The fuzes of the period were so crude that spherical case was seldom used when targets were rapidly closing and opening the range. A round for a 12-pounder contained 78 musket balls…. A round for a 6-pounder held 38 balls with a 2.5 ounce burster."

As for Gibbon, you forgot to mention that near the close of the ACW he commanded the 24th Corps in the Army of the James. It was he and his troops, plus a division of "Colored Troops" from the 25th Corps, plus, of course, Sheridan's cavalry, and later the 5th Corps, who got across Lee's path at Appomatox and forced him to surrender.

As for the ball rising after leaving the barrel, that would depend primarily on how level the barrel was with the ground (though windage could cause the ball to just happen to be rising slightly at the instant it left the barrel — not likely, but possible.) However, it could rise a couple of feet without ever rising far enough to pass over the heads of standing (walking/charging) men — provided the gun and the men were on the same level of ground. As long as the trajectory never rises above head-height it should be pretty difficult to miss a target as large as a battalion of infantry or a squadron of cavalry. (Assuming that the smoke from previous shots doesnt keep you from seeing them.)

M. Gandalf spoke of the "line of fire".
So, one must not, in error, think of the line of sight for an observer, nor even of the line of metal (the top line of the gun tube) in such case as the bore is not centered (either accidentally or intentionally) in the tube.
Then thinking only of the true line-of-fire ….
If one wanted to see the "miracle" of overcoming gravity , and seeing the ball rising above the line-of-fire, then there must be lift. The ease with which spherical spinnning or flying masses may be lifted is indexed by the "Mass Ratio" : the mass of the object divided by the mass of an equivalent volume of air. So, a beachball has a low mass ratio and a cannonball a high one. Hence we see in the textbooks the cannonball used over and over as the limiting case where their is no such lift.
Now, I must disagree with M. Gandalf when he states that the parabala is the form of the trajectory. This is merely an approximation. The correct shape is really a arc or segment of an ellipse, with the center of the earth as one of the foci. This is because the gravity (downward vector) is exerted through the center of the mass a body.
I do not think the differnce between the parabalic estimate and the elliptical path is even 1/10 of the width of the cannonball at up to 1000 yards, but I wanted to be precise.
In any case, cannonballs doreally fall to earth, and this really does start as soon as they are fired, with no rising in it at all, which was M. Gandalf's main point.

- just g

I remember in a Histroy Channel show On Math that a famous British prof in the 1740's did what came to be Secret studies.

He figured that guns used to much powder and that the ball flew flat. before this the optical illusion looking at the ball flight makes it appear to rise. He shot it through cloth. Every nation in this period did thease studie as science was newely applied to gunnery. I think he did the firist gunnery tables.

Lord Ghee

Don,

Sorry for the error of ommission on Gibbon.

Sincerely,
Kevin

Line of sight and line of fire (the path of the round) were not the same with smoothbore and early rifled artillery. That was the reason for the computation of point-blank, which is defined as the second time the round crossed the line of sight and was necessarily close range. It is defined in all of the Napoleonic and earlier period artillery manuals that I have or have seen, and it is also defined in Gibbon.

Sincerely,
Kevin

To add a further reference:

Brent Noswothy: Battle Tactics of Napoleon and His Enemies.

Hi

Hmmm.

Backspin to make a rising ball? I have done that playing tennis…but I cannot figure out how to put backspin on a rifle or cannon ball!

R

I wouldn't recommend any of Nosworthy's books as reference material. They are not as accurate as they could be. I've read all three, and compared with other works on the three periods he covers, he is far from the best.

Sincerely,
Kevin

Hi rocky,

Its works the same for a cannon ball as a tennis ball, you apply an acceleration (or deceleration) off centre.
It works most noticeably with less dense objects than cannon balls. The study by Robins published in 1742 was done with musket barrel bent slightly to the left. Screens of paper at various distances showed the ball to fire to the left as expected but after a while the ball curved back in and crossed back to the right.
This is because in exiting such a bent barrel the ball has been decelerated on its right side giving it a spin to the right which acts as a force to pull the ball to the right.

One of the points of rifling as in being held in the grooves the projectile cannot assume a different rotation.

Admitedly for a 12lb cannon ball the effect of a backspin might well be so negligible as to be unnoticeable.

Bentons tables give a muzzle velocity of about 450m/s for field artillery – which sounds fast enough – except there is gravity dragging it down at 9.8m/s/s – which I make a drop of about 5m in the first 500m; or if the line of shot / bore was placed exactly parallel to the ground and was 1m off the ground then the ball would hit the ground less than 200m from the barrel. So I make you definitely needing to be firing upwards a fair bit to make a first graze at over 500m
I am sure someone will correct my maths if its badly wrong.

JL

Got to wonder whether the powder charges used then were capable of burning fast and evenly enough to avoid applying some kind of spin, even when using a sabot.

Gents,

Sorry, just can't let this one go by.

The discussion from Gibbon refers to the axis of the gun tube, not a horizontal line drawn through the muzzle.

There is no back spin, bent barrels, or anything else involved. The reason the shell rises above the horizonal is that the axis of the gun tube is elevated above the horizontal.

This has been true for any artillery piece ever made, from torsion catapults to nuclear-capable self-propelled howitzers today.

The projectile starts to drop below the axis of the tube as soon as it leaves the barrel, but, we artillerymen being such crafty, low-borne, mechanically-oriented ne'er do wells that we are, elevate the axis of the tube above the line from the gun to the target. Back in Gibbon's day, that would have been only a couple of degrees above the horizontal; in the 20th and 21st centuries, with indirect fire being all the rage, we tend to elevate the axis of the tube way above that, sometimes well in excess of 45 degrees.

Backspin. Holy Moly. I need an aspirin.

- Bob McDonald, formerly of the 3rd Field Artillery (USA)

Bob,

I couldn't have said it better myself. Well done.

Sincerely,
Kevin, formerly of 10th and 12th Marines, two of the four Marine artillery regiments in the service.

Well that's the US Army and the US Marines Corps represented and as (I understand) the US military is the mutts nutz in the area of Arty that should wrap it up.

On the other hand if your all Soooo good, why can't you do back spin eh, c'mon why not? never mind the old impossible physics nonsense and all that defeatist claptrap, how about a strong updraft of wind, imaginative use of magnetism, levitation and strength of will, group hypnosis, winged ammunition, clever use of mirrors, the possibilities are endless.

Honestly I don't know what the modern military are up to I really don't; you need to pull your socks up the lot of you.

Call yourselves Wizzards ?

:)

If you find the idea of spin effecting a round object flying through the air ludicrous I guess you never played baseball or cricket.
With the momentum of the objects involved its more important in musket balls than cannon balls as I stated. The researchers in the 18th and 19th Century used practical experiments to look at the outcomes. These are available in works such as Scloppettaria and Robins New principles of Gunnery.
A modern synthesis of such works can be found in Halls Weapons & Warfare in Renaissance Europe; which despite its title uses data and published works from later on to get some idea of how these weapons performed, there apparently being no proper modern studies of the ballistics of such weapons.

JL

Well, actually ….

Tube-fired cruise missiles, rocket assisted rounds and all sorts of other stuff in the the US "arsenal" fly around rather nicely.

But even the most modern kinetic-kill electro-magnetic rail-gun that fires an un-powered projectile that has no airfoil shaped structures sees its round immediately fall from the line-of-fire. That gravity thing is a real design constant.

- g
(on behalf of the US defense technology and industrial base … keeping our warfighters supplied, while not breaking any laws of physics)

Hi

Bob and Kevin… well, I wasn't going to jump in as you guys did. Partly I wasn't sure I actually understood what was being presented!

1500fps with unpatched ball and the usual windage looks suspect to me as well. Getting that on the chronograph usually requies me to patch and have a good seal on the patch.

dunno'.

Rocky

Rocky Russo is that a musket you are talking or artillery piece.

Assume it is a musket

what is it max range and range at level.

a loaders book a friend let me burrow states 200m level at 5 ft (shoulder)

thanks

Lord Ghee

Lord Ghee

Never played cricket, but plenty of other sports. Clearly spin affects flight. However, I was not in the habit of launching my baseball, football, tennis ball, or golf ball with a smooth bore cannon. (Boy, there's an idea for you: combine re-enacting with batting cages.)

A smooth bore cannon is as likely to put spin on the ball in a bad direction as a good one; which is, after all, the reason some crafty bastage thought of cutting spiral grooves in the barrel, to put *predictable* spin on the projectile. Like in American football (i.e. not what Americans call soccer.)

Which spin, by the way, causes the projectile to hook (smoothly and predictably) to one side. In US-made artillery, it hooks to the left (alhought they actually call this "drift", not "hookage"), and so the fire direction center knows to lay the tube so many mils to the right of the target (depending on range).

But — if you want to correct for the fact that the ball/shell is dropping from the axis of the tube, you elevate the tube; you don't try to put backspin on the projectile.

Hi

Lord Gee, not sure I get the question.

The ball will fall at a rate of 9.8m/second per second.

The muzzle velocity is a big variable. Early smooth bores from 1450s to about 1720 were usually shot unpatched(exceptions being turkish janisarries with silk and perhaps italians), and the idea of "corning" powder hadn't been invented yet. So, assume muzzle velocities of ca 200m/s for pistols, and 300m/s for long guns and do your own sums. Those would be "optimum". After this with the paperpatched prepared cartridge, assume ca 350/400 m/s.

As you can see, 5 feet come up very quickly. Thus, there is no direct point of aim for the weapons.

There is an early 18th century series of actions where a 'modern' russian army was trying to combat the crimean tartars who realized they could stand at about 120m and shoot down the line infantry who would regularly put their balls in the ground at about 100m. THAT is a training problem. You could, theoretically, lob a round ball at some impressive ranges at a high angle. THAT is a long post I won't do here. The short version, however, is that the moa of the round is such that a hit would be a likely as doing a magic spell and calling down lighting as a tactic.

Rocky

Quote From RockyRusso

"1500fps with unpatched ball and the usual windage looks suspect to me as well. Getting that on the chronograph usually requies me to patch and have a good seal on the patch"

this is based on a Musket or due you own a Cannon.

I want a cannon.

Lord Ghee

Hi

Nope, it is based on the theoretical limits of black powder.

It takes near ideal seal and conditions to get this velocity.

R

The problem with black powder, as I understand it, is that it burns too fast. Poof! and it's gone. the shot or ball gets one kick and that's it. Modern powder burns more slowly, giving a continuous push up the barrel (thus the longer the barrel the greater the velocity) until all the powder is consumed. I believe various 19th Century boffins tried to slow the burning of black powder by using different sized of grains, etc., but with limited success.

And, of course, windage lets some of the force from the burning powder escape, which is why rifled guns actually needed less powder than smoothbores — less windage.

Hi

Well…sort of. What you are thinking of is called "corning". I will try to explain. Initially, you mix powder as a mud type liquid and dry in a sheet. But you cannot use it until you break it up in some form. Usually this is just crushing the powder. By the nappy period, there had developed techniques for "corning" producing a consistant SIZE to the corns and using different sizes for different application. You generally want a finer powder in a flash pan or a pistol than in a 32#er!

And part of the process sort of smoothes the surface that reduces it speed in absorbing water from the atmosphere.

Anyway, for "Lord"s point. Powder is limited in pressure and speed of burn in that its upper limit is such that more than about 1700fps is just not going to happen. Throw in windage of 4 to 10 % and the theoretical limit starts dropping to subsonic speeds.

One problem with older sources on these weapons is that the muzzle velocity had to be guessed at. These days we have the equipment to precisely measure the speed of the projectile as it leaves the barrell.

Rocky

The ballistic properties of modern nitrocellulose type propellants are completely different from black powder. This is one reason why comparison between modern artillery and black powder cannon is like comparing apples with chalk.

Unlike modern weapons, a longer barrel with a black powder cannon does not mean longer range because maximum velocity
is always generated at about 18 calibres – that is 18 times the diameter of the bore. This means that there is an
optimum length for all calibres of cannon beyond which it is a waste of metal.

Smoothbore cannon were also innacuate because of the windage, that is the difference between the diameter of the
bore and that of the round short, which caused bouncing as the ball moved down the bore, called balloting or
coroming. This was unpredictable and imparted spin through all axes resulting in an erratic trajectory to left or right, or floating where the shot rose. The concept of a flat trajectory with black powder smoothbore cannon is a theoretical illusion which, if it happened at all, was accident rather than design.

The use of bronze alloy for gun founding had nothing to do with accuracy or range and everything to do with strength
because the alloy was more elastic than iron and examination of the alloys in use shows that the composition of the metal in the best guns changed little from the 16th century to the end of the bronze cannon era in the mid 19th century.

What changed was the understanding of ballistics and the the properties of the material. The reason why guns tended to get shorter and thinner was threefold. First, it was realised that thickness could be reduced without loss of strength. Second, it was realised that length did not mean longer range and finally, smaller guns minimised the unnecessary use of expensive alloy. The length of bore relative to the thickness of of the barrel wall and
calibre are indicative of the founders expertise in these contexts. The heavier the weapon is in its class, the inferior it generally is as a reflection of the designers understanding or the founders skill.

JC

According to the opening posting and the artillery manual quoted, which applied to smoothbore cannon and black powder, the ball doesn't rise above the line of fire.

Seems Gibbon knew what he was talking about. He was a quite competent artillery man and proved himself both theoretically and on the battlefield.

I have seen no contemporary evidence that refutes him.

Interestingly, the same thing is taught today at Fort Sill, the US Army artillery school where both Army and Marine Corps artillerymen are taught, along with foreign students. The bottom line is that the projectile does not rise above the line of firing.

Sincerely,
Kevin

"This was unpredictable and imparted spin through all axes resulting in an erratic trajectory to left or right, or floating where the shot rose."

Please provide the calculations that indicate that the spin imparted by carooming caused the ball to rise, or the source from which you have the quoted information.

I believe you are greatly mistaken, but would be happy to learn how this "floating" can happen.

g

>"The use of bronze alloy for gun founding had nothing to do with accuracy or range and everything to do with strength…"<

And with weight; bronze is lighter than iron. Iron was used for rifled guns in the ACW era because the rifling in a bronze guns soon wears smooth (which didn't keep them from trying it; the 12-pounder James Rifle of the ACW was just a pre-war 12-pounder smoothbore that had been rifled).

Iron was also used because bronze is relatively expensive and iron was plentiful in the United States.

Iron also rusts, whereas brass does not.

Sincerely,
Kevin

Interested to see that Fort Sill still teaches black powder concepts – how quaint:-) The difference between modern artillery and Napoleonic artillery is about the same as that of a Handsome Cab and a modern London Taxi – both fill the same role but are otherwise rather different.

Be that as it may, I suppose one could start with the opbservations of Venitian gunners of the 16th and 17th Centuries. Then there is Robbin's New Principles of Gunnery (1742 as I remember) and the work of Heinrich Magnus on external ballistics in the mid 19th century. I am afraid the maths is not reproduceable in this medium.

This was confirmed in the context of smoothbore black-powder artillery by experiments conducted in 1851 with a 10 inch gun and specially made excentric shot.

In essence the windage meant that that the gas produced by the decomposition of the black powder could act on either
the top or bottom of the shot, increasing the caroming as it travelled down the bore, and spin, thus increasing the intrinsic innacuracy of smoothbore cannon generally. This all meant that the attitude of the shot as it exited the tube was not predictable, and spin could be produced through any axis, though this was certainly reduced towards the mid 18th Century by reducing windage to a minimum.

Having identified that spin imparted certain haracteristics to the flight of projectiles, the next step was to harness and control this by rifling. The concept of a round shot exiting the tube in a predictable way, including a consistent flat trajectory at 0 degrees elevation is an illusion which assumes that the the gas acted equally and exactly on the base of the shot and no caroming took place.

JC

Robins did not experiment with artillery rounds, but with musket rounds.

No one has stated that roundshot has 'a consitent flat trajectory at 0 degrees elevation.' What has been said is that as soon as a round is fired from an artillery piece, the round starts to drop from its line of fire.

Primary source material from artillery manuals involving gunnery has been given. If contradictory evidence is available then it should be shown. All that has been offered to counter primary source artillery material is opinion. Therefore, there is nothing to contradict what has been given from Gibbon.

As for Robins, this extract is from Engineering the Revolution by Ken Alder, pages 104-107:

'First was the problem of scale. Robins had done his experimental work [on muzzle velocity] with musketballs…Not until 1755 did Charles Hutton carry out some tests at Woolwich using Robins' methods with 6-pound balls.'

Euler remarked on Robins that 'The truth had less to do with [Robins'] research, that the need to square the results of his theory with those of practice.'

Again, the bottom line is that an artillery round does not rise above the line of fire. This is elementary gunnery and ballistics.

Sincerely,
Kevin

Hi

Ok, ok, calm down. Everyone is right here.

Simply, in a theoretical sense, all fire is define by a cone projecte from the barrell. Modern equipment can be as accuate as a cone one minute of angle across.

Which means up.

In the napoleonic period and before, real world tests seem to show an "oval" that is the cone is "wider" than it is high. Simply, random missing means that the miss is usuall left or right rather than short or long. Long, short would be more expectable if the cone was perfect.

Similarly the cannister elipse is an elipse rather than described by the base of a "round" cone.

Rocky

>"… random missing means that the miss is usuall left or right rather than short or long. Long, short would be more expectable if the cone was perfect…."<

Yeah, but when firing at a target the size of an infantry battalion or a cavalry squadron a miss of a few feet to the left or right is usually still a hit. Whereas a miss of a few feet too high is a miss indeed (unless it happens to hit another battalion/squadron coming up behind the targeted one). A miss of a few feet too low might still be a hit if the ground is hard and flat, allowing the shot to ricochet.

Who is exited? :-)

I am reminded of the claims of Herman Moritz, a 16th century philosopher who believed that as gunpowder was clearly the invention of the devil, shot was propelled by a demon that sat astride it, which clearly indicated that they could not be spinning because if they were, not even a demon could hang on :-)

An object experiencing only the force of gravity will behave as an 'ideal projectile'. The projectile moves with constant velocity in the horizontal direction and with the constant acceleration of gravity in the vertical direction. This only true, however, if air resistance is ignored and in practice air resisitance modifies the motion of all objects moving through it.

Robbins was not called the father of moderd ballistics for nothing and much of what was disputed in his lifetime was shown to be right 100 years after his death.

However, I have been here before and got the T shirt – my interest is diminishing.

JC

Dear JC :

Since sources or calculations indicating how the alleged "spin" imparted by carooming could be sufficient to cause cannonballs to "float" did not spring to your recollection, may I ask you instead for some information on the process of the caroom itself ?

It is not clear to me that the process of decomposition of the gunpowder would cause the cannonball to bounce its way down the bore. Rather, since air compresses so much better than iron, it occurs to me that the pressure exerted in the windage might be sufficent to keep the ball roughly "centered" and not banging its way down the tube. Otherwise, one might think that there would be a loud screech or clanging upon each round being fired – something I had never heard described in a memoire. Similarly, one would expect various scratch marks to be visible mear the mouth of the piece, at the point where a harder ball made its final "bounce" before departure. I do not recall seeing this. Or, if the tube is harder than the ball, one would expect to see the rounds flattened, or scratched. Again, I do not recall this.

So, since you have described all this "carooming", can you provide a modern empirical source that describes this effect (based on modern instrumentation) or a calculation that indicates that the ball is not suported by or moving in a torus of compressed air as it travels the barrel ?

I might note, contrary to your prior post, that these are matters of INTERNAL ballistics, and that Magnus effect is seen in external ballistics. Specially, the Magnus effect is not, to my knowledge, ever even of the same order of magnitude as the effect of air resisitance and atmospheric wind (let alone gravity). However, since the Magnus effect does act about the center of pressure, not the center of gravity, it can cause a "bullet-shaped" round to yaw very slightly, and thus change the angle of incidence of its resulting impact . This might have some relevance to the design of kinetic kill rounds or possibly shaped-charge anti-armour rounds – but I cant see how it even in theory has any impact on a round cannonball.

Perhaps you could either expand on your prior post or provide a source where a more detailed discussion of the Magnus effect and cannonballs can be found.

Thank you.

-g

'I have been here before and got the T shirt – my interest is diminishing.'

Yes you have and of course it is, for two reasons: first, you can provide no evidence (as was the situation before), and second, because you are wrong.

Sincerely,
Kevin

>"…which clearly indicated that they could not be spinning because if they were, not even a demon could hang on."<

Which just goes to show how little he knew about the adhering properties of demons!

>"… since air compresses so much better than iron, it occurs to me that the pressure exerted in the windage might be sufficent to keep the ball roughly "centered" and not banging its way down the tube."<

Excellent point. But it occurs to me that, gravity being what it is even inside the gun tube, that there would be little or no windage at the bottom, more at the sides and most at the top.

Dear donlowry :

Actually, the absence of a smear, scratch, flattening, screech, clang, etc. is quite diagnostic (recall that cannon balls were oft-times collected for reuse). I am actually rather confident about my supposed pressure wave and its ability to to "center" the cannon ball.

Now, with a really badly out of round ball, or a terribly made charge or a gun with a large-ish void in the wall of the bore … these could make all sorts of carooms possible. But these would be sorts of "errors", not typical and not by design.

Next, even in the compressed torus of air in the windage, the ball will tend to slew based on normal irregularities in its roundness, its center of gravity, the decomposition of the charge, the small-ish voids in the wall of the bore, etc. But these effects will be only to "bounce" the ball a little closer or further from one point in the windage to another. Thus this movement will be slight, and the source of "spin" will be the interaction with the the compressed mass of air, not a bounce off the side wall of the bore.

Also, I take your point re: gravity … but condsider that the ball begins in the "bottom" of the windage and so its first vector of movement (other than "straight" down the center of bore) will be "up" .

So, overall, I think the amount of the carooming is quite small, and it is against air, not the sidewall of the gun and that the potential to impart spin is correspondingly low and the resulting lift from spin essentially zero. Overall , if the resulting lift was enough to "lift" the ball from the line of fire by its own diameter, I would be quite surprised.

Lastly, the "appearance" of rising above the line of fire is easy to understand :
> in the case of a "leveled" horizontal piece, the actual bore or line of fire is titled up with respect to the line of metal
> and, especially in the case of an elevated piece, the wind – even assuming it is blowing parallel to the ground – may "push" the round essential above the line of fire.

In general, in orders of magnitude and for "typical" or "as designed" guns :
> the force of the inital charge and gravity are the main effects
> an order of magnitude lower, but still noticable, would be wind and atmosheric conditions
> at least another and perhaps more orders of magnitude lower and not noticable would be lift from spin imparted by any kind of caroom

Or at least thats how I was saw it. Of course, I would be very interested in calculations showing a contrary result.

g

Dear just g,

You asked for sources for caroming?

Muller. A Treatise of Artillery 1780, p40.
Roberts. The Hand-Book Of Artillery for the Service of the United States, 1863 p87.

In case you don't have either try Prof Guilmartin. The Guns of the Santissimo Sacremento. You can find this article on his web site. He describes caroming, which he calls balloting, and the way shot drifted and floated.

Also go to the Naval Historical Centre – The Bronze Guns of Leutze Park – link and look under the glossary entry for windage.

Caroming wore out bronze guns and although reducing windage helped, so long as the shot was smaller in diameter than the bore, it remained present

Yes, you are quite right, the work by Magnus was concerned with external ballistics but your point in this context eludes me. Internal ballisitcs are concerned with what happens within the tube between ignition of the propellent, production of gas through decomposition, build up of pressure and the passage of the projectile until it exits the mouth of the piece. External ballistics are concerned with what happens during the flight of the projectile until it hits its target, and terminal ballistics are the effect on the target. There are a number of sites on the web that discuss the Magnus effect and round shot specifically – I'm afraid I don't understand the mathematics.

In addition there is a research group in Scandinavia – Demark I think – which did some work on the flight of shot using radar to capture the information.

I think it is a mistake to attempt to relate what happens with modern artillery natures in flight to those of round shot.

JC

Herman Moritz was clearly badly informed. As demons are supernatural they are able to negate the forces of nature. Everybody knows this:-)

JC

John Cook: The little devils!

just g: What you say sounds right. I'm no expert, and I hold no brief for either side in the "rising shot" debate. With that said, let me add a "however": Since black powder burned so quickly, would the blast of wind through the windage (is that how it got its name?) have died out or diminished significantly before the shot reached the muzzle? If so, good old gravity would rule again from that point on. Just asking, as I have no knowledge or anything to base a guess on.

'You asked for sources for caroming?

Muller. A Treatise of Artillery 1780, p40.'

And the quote is…?

Sincerely,
Kevin