Famous Monitor's XI-inch Dahlgren Shell Guns

trice · Oct 28, 2022

Saphroneth said:
See my previous post. The gun is whatever gun Dahlgren has where he noticed whatever this effect was.

Perhaps it was a 64 pounder, which has a muzzle velocity easily into the supersonic range, but I don't know for sure - but if Dahlgren was noticing this effect, obviously he's noticing it on a gun that actually exists and that he's testing.

Again.

He takes that gun, whatever it is, and fires it ten times at maximum safe powder load at 2 degrees elevation. He notes down the range each time. There is some mean range from those observations, which forms an empirical range.

Then he fires it an eleventh time.

Does the range he gets accord with the results of the empirically derived range, or not?

Once again, your approach is blinding you to the real-life situation.

Dahlgren is looking at current guns and trying to design improvements for them. Whatever he has as data on existing guns is only meaningful as a guide to what the design for the future should be. This is the context for his statements. Whatever you are seeking with your approach, it is not what the gun designer of that day is seeking. If you wonder why you are misunderstanding what he says, look in the mirror.

Saphroneth · Oct 28, 2022

trice said:
Once again, your approach is blinding you to the real-life situation.

Dahlgren is looking at current guns and trying to design improvements for them. Whatever he has as data on existing guns is only meaningful as a guide to what the design for the future should be. This is the context for his statements. Whatever you are seeking with your approach, it is not what the gun designer of that day is seeking. If you wonder why you are misunderstanding what he says, look in the mirror.

But this whole thing comes from the idea that high velocity guns are inaccurate.

So with whatever high velocity gun that Dahlgren discovered this effect on, if he fired the gun at 2 degrees elevation at 1,400 fps (or 1,600, or whatever) ten times to get an empirical range, and he then fired the gun an eleventh time, would the gun's performance match that empirical range or not?

It is a yes or no question.

Saphroneth · Oct 28, 2022

So to explain why I think that, there are basically two possibilities here.

Possibility one is that Dahlgren's comments on high velocity guns being inaccurate are based on observational data. If that is the case, he has a high velocity gun he has test-fired and observed the data for.

So, that's the gun I'm asking about.

Possibility two is that Dahlgren did not have a high velocity gun at the time, and so couldn't do the empirical range table I'm talking about.

But if that's the case, then he didn't base his high-velocity gun-inaccuracy principle on any data - he just thought it up and decided it was true.

It has to be one of those things. Either Dahlgren had a high velocity gun, or he didn't and made the whole thing up.

Assuming that Dahlgren didn't make the whole thing up, then:

Saphroneth said:
So with whatever high velocity gun that Dahlgren discovered this effect on, if he fired the gun at 2 degrees elevation at 1,400 fps (or 1,600, or whatever) ten times to get an empirical range, and he then fired the gun an eleventh time, would the gun's performance match that empirical range or not?

Saphroneth · Oct 28, 2022

In the hopes that I can make my point reasonably, here's the thing.

It does not really matter, for the aiming and firing of a gun, whether you fully understand the principles behind what is causing it to act the way it is.
What matters is that you understand the extent to which the factors under your control (powder load, elevation etc.) affect the result (the point at which the ball strikes a prospective target).
A range table is basically a list of those things, and the expected results. It can be derived entirely empirically from actual test firings, and reflects to the extent of your measurement the way in which the combination of those factors you can control affect the result.

It does not mean that you know exactly where a given projectile will strike the ground. There are still random factors (which are inconsistent across firings, such as wind or the spin on the ball) which mean that the actual hit location is randomly distributed about the projected hit location.

But the varying drag behaviour of a high velocity cannonball is not random. It is not inconsistent across firings. And you don't need to understand it to make and use a range table.

So. Take a high velocity gun, fire it ten times at 2 degrees, and you have a range value. And if you fire it ten more times, you'll hit at points distributed about that point of aim.
In other words, it will be accurate.

trice · Oct 28, 2022

@Saphroneth,

You are trying to prove something to yourself that has nothing to do with the real life situation. As a result, it has nothing to do with what Dahlgren was doing and saying. If you wonder why you can't find whatever it is you are looking for, this is why.

Saphroneth · Oct 28, 2022

trice said:
You are trying to prove something to yourself that has nothing to do with the real life situation. As a result, it has nothing to do with what Dahlgren was doing and saying. If you wonder why you can't find whatever it is you are looking for, this is why.

Well, then, how exactly did Dahlgren discover this inaccuracy in high velocity guns?

Did he do it by finding an empirical range-table result for a high velocity gun, and then finding that the high velocity gun didn't actually hit at the empirical result?

Or did he calculate a range-table result for a high velocity gun, and then find that the high velocity gun didn't actually hit at the calculated result?

There's not many other options for how Dahlgren could have discovered this inaccuracy.

trice · Oct 28, 2022

Saphroneth said:
Well, then, how exactly did Dahlgren discover this inaccuracy in high velocity guns?

Did he do it by finding an empirical range-table result for a high velocity gun, and then finding that the high velocity gun didn't actually hit at the empirical result?

Or did he calculate a range-table result for a high velocity gun, and then find that the high velocity gun didn't actually hit at the calculated result?

There's not many other options for how Dahlgren could have discovered this inaccuracy.

Sigh. Please review the many posts before this.

I have told you what Dahlgren was doing: test-firing the guns from the USN 1845 standard (actually, test-firing them with a new sight). I have told you that he was tracking the shot and trajectories as best he could (he was a Lt., new to the Ordnance, applying techniques from his days in the coastal survey work). He almost died doing those test-firings (which non doubt strengthened his emphasis on safety). His 1849 report and 1850 letter are presenting his conclusion, that at some point the higher velocity is too high and results in inaccuracy for the gun.

He carries that forward into his design for a new gun (the January 1850 IX inch design proposal). This is his soda-bottle gun design (as the British called it). If one of his guns burst, he wanted it to be at the chase end of the barrel, not the breech. His guns are designed that way because of his concentration on gun safety and service life, which also favors lower powder charges. His guns are big and fire heavy shot. He is trying to emphasize the weight of the shot to make up for the lower muzzle-velocity -- and he feels that the lower muzzle velocity will also improve accuracy.

Almost all design work in any field is based on compromises and trade-offs the designer must make to get the product done. If it is not done that way, the practical result is that most such designs will never be produced. This is simply how the real world works.

Dahlgren was very successful at gun design. Overall, his guns were extremely safe with long service lives. Generally, other guns by other people were not as safe and had shorter service lives in Civil War experience.

While there would have been some benefit to refining and publishing improved range charts, it would have been minimal. The 1845 standard guns were inadequate to the needs of the Navy. Dahlgren was trying to improve by replacement with new designs -- and he pushed and prodded the USN into the future to do it.

67th Tigers · Oct 29, 2022

trice said:
Sigh. Please review the many posts before this.

We keep asking, because you haven't answered. Can we have references?

Saphroneth · Oct 29, 2022

trice said:
I have told you what Dahlgren was doing: test-firing the guns from the USN 1845 standard (actually, test-firing them with a new sight). I have told you that he was tracking the shot and trajectories as best he could (he was a Lt., new to the Ordnance, applying techniques from his days in the coastal survey work). He almost died doing those test-firings (which non doubt strengthened his emphasis on safety). His 1849 report and 1850 letter are presenting his conclusion, that at some point the higher velocity is too high and results in inaccuracy for the gun.

Okay, but surely you must realize that the inaccuracy can't be from any effect that is consistent, right?

If Dahlgren fires the gun at 1,400 fps and decides that it's inaccurate, then that must result from the gun behaving differently than he is expecting - either in terms of range, or in terms of deviation.

But if the cause of this effect is the increased drag at transsonic velocities, then it's consistent from firings. Dahlgren could have fired the gun a hundred times at the same muzzle velocity and it would have had the same range every single time, because the effect is consistent across firings.

That is why I kept asking that question, which you have consistently failed to answer. I have been asking it because I want to be absolutely sure that I am not attributing the wrong viewpoint to you, but since you have failed to answer it I will be assuming that the answer is:

Yes

Question:

Saphroneth said:
He takes that gun, whatever it is, and fires it ten times at maximum safe powder load at 2 degrees elevation. He notes down the range each time. There is some mean range from those observations, which forms an empirical range.

Then he fires it an eleventh time.

Does the range he gets accord with the results of the empirically derived range, or not?

I am now assuming your answer is yes - that the range he gets does accord with the results of the empirically derived range.

That means that the gun is not inaccurate. It behaves consistently. It just needs a range table which allows for that muzzle velocity, and Dahlgren is wrong.

No

I am now assuming your answer is no - that the range he gets does not accord with the results of the empirically derived range.

That means that the inaccuracy does not come from the increased drag. It comes from something else that is different in different firings, and you have not said what that is. (It could be that the recoil is too large for the gun and so it's being jerked backwards too much during firing, and that this is affecting the trajectory, as discussed in the 1855 treatise.)

Feel free to pick whichever of these two answers you prefer, but your position - that Dahlgren correctly observed inaccuracy and that this is from increased drag at high velocities - is fundamentally inconsistent.

Saphroneth · Oct 30, 2022

So I thought it might help to lay out why it's important to get the details, and if possible the magnitude, of the inaccuracy effect at high velocities.

When going from a higher velocity to a lower velocity, ignoring only this unknown inaccuracy effect, there are several disadvantages that accrue, along with a couple of advantages.

Advantages.

A lower velocity ball needs less powder to fire it, and is thus cheaper.
It is less likely that a given design of shell will rupture. (This is specific to shells.)
The strain placed on the gun is less, which can be an especial advantage if your metallurgy is not up to producing strong guns.

Disadvantages.

The gun is more accurate at higher velocities (ignoring the unknown inaccuracy effect as mentioned above) because the Magnus effect and the influence of wind have less time to act on it; if this scaled linearly with time, this would roughly mean that double the average velocity to target reduced the average deviation from the expected impact location to 50% of the previous value. Given that the magnus effect is not as strong at very high velocities (owing to a lack of asymmetrical vortices) scaling linearly with time may not be correct.
The ball strikes with greater force at higher velocities.
The target has less time to move out of the way.

These last few have real tangible impacts, and they can be measured.

To take the striking force first, and referring it to naval matters, the sides of a first-rate ship of the line can be up to three feet of oak in thickness. Dahlgren's table of penetration by various guns indicates that with 32 pounders (firing shot), a muzzle velocity of 1700 feet per second results in the 32 pounder being able to penetrate 38.7 inches of white oak at 500 yards, while a muzzle velocity of 1,250 feet per second results in penetrating only 26.4 inches of white oak at 500 yards - the difference between punching through the sidewalls of a ship of the line and having the ball lodge to no impact - and the 1700 feet per second 32 pounder can penetrate as well at 1,000 yards as the 1250 feet per second 32 pounder can penetrate at 500 yards.

While Dahlgren could not have known to consider the possible impact of ironclads, the impact is actually more noticeable with them. Comparing a 1500 fps muzzle velocity with a 1000 fps muzzle velocity, there are ships which a 1000 fps muzzle velocity 11" gun cannot penetrate at the muzzle (which is exactly defeated by 3" of single plate wrought iron at the muzzle, by the Fairbairn formula) which the 1500 fps muzzle velocity 11" gun could penetrate at any range less than 1,200 yards (which is the range at 2 degrees elevation, though this is basically by chance).
This is a difference (penetration versus not, terminal effects versus not) over practical battle ranges, and not a small one.

For flight time, a target at 1200 yards requires 2 degrees of elevation at 1500 fps (and takes 3 seconds) while at 1000 fps it requires 4 degrees of elevation (and takes 4.1 seconds). This reduces deviation in the assumption above by 25% going from the lower muzzle velocity to the higher one (3 versus 4 seconds) and for a ship moving at 12 knots that's about a 6 metre/7 yard difference in target position. Granted that the target will have moved 18 metres anyway, but for a Liffey class frigate that's about another 8% of her length and for a smaller ship it's more.

1500 fps is by no means the greatest possible velocity, either, and the 1700 fps of the 32 pounder (or the 1800+ fps of the 68 pounder) would amplify all of them further. By 1800 fps a 1,200 yard shot takes only 2.5 seconds and requires less than 1.5 degrees in elevation.

Saphroneth · Oct 31, 2022

I think there's an argument to be made that a key error (or conceit) that Dahlgren had in the 1850s was that there should only be one powder charge for his guns. The authorized charges for other guns of the time (shell guns and shot guns both) had different charges for "distant", "ordinary" and "near" firing, with the 64 pounder of 106 cwt being able to take 16 lbs of powder in distant firing, but the authorized charges for the Dahlgren guns had only one value; this didn't change until the aftermath of Hampton Roads, where all Dahlgren guns above 8 inches had larger far charges authorized.

Sometimes you don't want to overstrain the gun or make a shell break in the gun barrel, but sometimes you do need higher velocity to reach a distant target, or to do so with sufficient force. Since the guns pre-Dahlgren had different charges, Dahlgren going to a single charge is a decision on his part and one which he later seems to have concluded was in error based on new information.

trice · Nov 2, 2022

No. You are wrong on all of this. While we are at it, no, Dahlgren did not believe " that there should only be one powder charge for his guns": this is just you making up strawmen to argue against. Abandon all this attempt to prove your own ideas are true to yourself.

Please stop all this nonsense. Pay attention to what was real, not what you imagine. Do actual historical research if you want to find out what a man like Dahlgren thought. Stop imagining things to argue against.

Saphroneth · Nov 3, 2022

trice said:
While we are at it, no, Dahlgren did not believe " that there should only be one powder charge for his guns": this is just you making up strawmen to argue against.

But there was only one authorized powder charge for each of the Dahlgren guns in 1861, and after Dahlgren's 1862 testing he recommended a larger powder charge and the Navy approved it.
What powder charge other than 15 lbs did Dahlgren think should be used on the 11" before Hampton Roads?

trice said:
No. You are wrong on all of this.

If you fire a cannon at 1400 fps muzzle velocity at 2 degrees elevation ten times, and average out where the projectiles land, that gives you an empirical range for that cannon at 1400 fps muzzle velocity at 2 degrees (e.g. 1000 metres), correct?

If so, and you fired the cannon at 1400 fps muzzle velocity at 2 degrees elevation, expecting it to land at that range, would your expectation be borne out or not?

If you know that I'm wrong about this, then you know the right answer to that question. But you keep refusing to answer it, and I genuinely think it would be helpful if you did.

Saphroneth · Nov 3, 2022

trice said:
Deleted

I am not trying to "find a way to ignore" what I have been shown; I am taking it into account and asking the questions which will lead to the next step of knowledge.

That is why I am asking the same question to you over and over again, because it actually does point to an important issue about the claim that it is increased drag at high velocity which causes high velocity projectiles to be less accurate - namely, that the effect of the drag is consistent and so all it should result in is a difference in point of aim.

Do you dispute that, or not? It is no good you asking me to review the entire thread, because you have not answered that question even though I have put it to you several times in different formats.

trice · Nov 3, 2022

Saphroneth said:
I am not trying to "find a way to ignore" what I have been shown; I am taking it into account and asking the questions which will lead to the next step of knowledge.

That is why I am asking the same question to you over and over again, because it actually does point to an important issue about the claim that it is increased drag at high velocity which causes high velocity projectiles to be less accurate - namely, that the effect of the drag is consistent and so all it should result in is a difference in point of aim.

Do you dispute that, or not? It is no good you asking me to review the entire thread, because you have not answered that question even though I have put it to you several times in different formats.

And yet, time after time, you make believe that you have not been shown the facts and try to insist that something else is true. Drop your point of view and try to examine what is said to you objectively. Look at facts instead of your own opinions. Do not make up reasons to claim someone like Dahlgren was wrong when you know, absolutely for certain, that he was on the correct path. Be more honest with yourself.

Saphroneth · Nov 3, 2022

trice said:
And yet, time after time, you make believe that you have not been shown the facts and try to insist that something else is true. Drop your point of view and try to examine what is said to you objectively. Look at facts instead of your own opinions. Do not make up reasons to claim someone like Dahlgren was wrong when you know, absolutely for certain, that he was on the correct path. Be more honest with yourself.

Then surely you should be able to answer the question I have repeatedly asked?

trice · Nov 3, 2022

Saphroneth said:
Then surely you should be able to answer the question I have repeatedly asked?

Matters have been explained to you many times. You refuse to acknowledge facts long since known to you. You evade and go off on tangents to avoid simple, clear, factual answers. Stop and review what you have already been shown. Answer the questions you never have. Be more honest with yourself and stop all this nonsense.

Saphroneth · Nov 3, 2022

trice said:
Matters have been explained to you many times. You refuse to acknowledge facts long since known to you. You evade and go off on tangents to avoid simple, clear, factual answers. Stop and review what you have already been shown. Answer the questions you never have. Be more honest with yourself and stop all this nonsense.

I'll try to explain in simple terms, then.

The effect that Dahlgren is observing falls into one of two possible categories. It is either consistent (as in, the same thing happens if you fire the gun in the same orientation with the same charge more than once) or it is random (as in, the scale and/or direction of the effect is significantly different each time the gun fires, and can range from no effect to maximum deviation).

If it is consistent, then that is something that can be entirely compensated for with the right kind of range tables. It's how modern high velocity (smoothbore or rifled) rounds can land on target from the first round, because just about everything about the firing can be predicted.
This means the gun is not actually inaccurate, the point of aim is just harder to calculate.

If it is random, then it's not something that can be compensated for, and higher velocity weapons are indeed more inaccurate. But the cause of this can't be the increased drag at high velocities that you've pointed to, because the increased drag at high velocities is completely mathematically predictable (with modern methods) and that means that its behaviour is consistent.

My asking these questions is not trying to "evade" and "go off on tangents". It is not "refusing" to acknowledge facts. It is trying to get you to explain why it is that a type of effect which is consistent is being given as an explanation for why a gun is inaccurate.

Saphroneth · Nov 3, 2022

And, just to be clear - when I say that increased drag at high velocities is completely mathematically predictable with modern methods, I am not expecting Dahlgren (or anyone else) to use modern methods to determine the drag coefficient a thousand times a second like the code I wrote is. What I am saying is that empirical range tables could be derived for a gun at a given muzzle velocity, and that these empirical range tables would describe the action of the projectile to within the limits of the variance caused by genuinely random factors (like the magnus effect and wind).

trice · Nov 4, 2022

See above.

Famous Monitor's XI-inch Dahlgren Shell Guns

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Major

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Colonel

Similar threads

Similar threads