Author Topic: wall-gun question  (Read 1143 times)

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Offline oltom

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wall-gun question
« on: May 09, 2011, 12:41:55 PM »
what twist would i make a 'wall-gun' that is 1" bore???
I saw a 1860's something wall-gun, and i believe i can duplicate her....... ;D
barrel was 4 ft or so....cap-lock, and had a remove-able breach section.....
but what twist for a 1" ball????
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Offline guardsgunner

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Re: wall-gun question
« Reply #1 on: May 09, 2011, 12:48:13 PM »
Was it hex bored?

Offline The Jeff

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Re: wall-gun question
« Reply #2 on: May 09, 2011, 12:55:13 PM »
You might try the Greenhill formula. http://en.wikipedia.org/wiki/George_Greenhill

If you're shooting a 1" round ball, I come up with 1:150.

Offline GGaskill

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Re: wall-gun question
« Reply #3 on: May 09, 2011, 01:22:41 PM »
If you're shooting round balls, Greenhill's formula will be too fast a twist, although probably not too too fast.
GG
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Offline Double D

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Re: wall-gun question
« Reply #4 on: May 09, 2011, 01:46:32 PM »
Weren't most wall guns justr smoothbore?

Offline seacoastartillery

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Re: wall-gun question
« Reply #5 on: May 09, 2011, 02:12:39 PM »
   " The Greenhill Twist Rate formula is not valid for round balls, either mathematically or physically, and the real-world reasons why rifling is beneficial for round balls are not predicted or modeled at all in Greenhill's formula."
_________________________________________

"I recently found an article in the International Journal of Impact Engineering where the author did just what I was looking for went back to Greenhill's original formula and examined his assumptions, models, and approximations.  Here's what I found after reading the paper and talking to its author:

1) The Greenhill formula assumes the air is frictionless, so it ignores any boundary effects such as turbulence. The formula also assumes that the density and shape of the projectile are consistent and flawless.

2) The mathematical model Greenhill used for the bullet is a "prolate spheroid" - a round shape where the length is longer than the diameter (think of a rugby ball).

3) Further, the artillery shells Greenhill was modeling in his work were about 2.5 times longer than their caliber, and all of the experimental data used to calculate the value of the constant 'C' in the simplified formula (usually given as 150 or 180) are from projectiles whose length was between 2.5 and 8.0 times longer than their caliber.

Since Greenhill chose to model the projectile as a prolate spheroid, many of his assumptions and simplifications don't work for round balls. When I asked the author about it, he agreed that the full version of the Greenhill formula gets "very strange" when the projectile length is less than about twice as long as the caliber. And when the length/caliber ratio gets down to 1:1 (as in a round ball), the full formula "blows up" entirely (some terms shrink to zero, while other terms go to infinity, so the formula gives no result.)

With all this said, there's no doubt that round balls benefit from a small amount of rifling in the barrel, but this is only because the balls are never perfect spheres, and the spinning motion helps "average out" the imperfections. There are also things like the Magnus effect, but the Magnus Effect would actually be an argument *against* rifling, since it states that a crosswind on a spinning projectile causes it to deviate high or low, depending on the direction of the crosswind. With a non-spinning ball, there would be no Magnus Effect. However, there's nothing in Greenhill's formula that takes into account imperfections in the ball or things like the Magnus effect, so it's not appropriate to use Greenhill's formula to calculate *how much* twist to use with a round ball.

If people are happy with the twist rates that Greenhill's formula gives them for round balls, I suspect that it's because the twist rate given by (mis)using Greenhill's formula in this manner is actually tighter than what's needed to correct for the imperfections in the ball. And having too much twist (within limits) isn't going to cause any problems."
     The info here is from a posting by Scott Riqui on the Firing line forum.  We know quite a bit about machinist's math, but this fellow is far more astute in the advanced math that you need to understand this topic thoroughly.  Why re-invent the wheel?

    The way we would approach an optimum twist is to calculate the proportional decrease or increase when going from one standard cal. twist to another standard cal. twist and then interpolate up to your 1.00" bore size.

Mike and Tracy

P.S.   Double D, is correct, of course, but there was some use of rifling even back then, so, while the vast majority were smooth bore, you could easily justify your decision to go with rifling.  Why was the Confederate Williams Gun, at 1.57" not rifled?
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Offline Artilleryman

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Re: wall-gun question
« Reply #6 on: May 09, 2011, 04:08:25 PM »


Is this the gun you are talking about?
Norm Gibson, 1st SC Vol., ACWSA

Offline guardsgunner

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Re: wall-gun question
« Reply #7 on: May 09, 2011, 04:28:36 PM »
Nope, Williams guns were not rifled in any of thier three sizes. An officer of the 66th Ill inf claimed that they were repeatng rifles but none were captured to rarify that. Buck shot seems to have been a common round and would not work well from a rifle.
Other guns of similar size, the Ellsworth ,Hughes and Travis guns are rifled. The Woodruff and Filley guns came rifled and smooth.
Whitworth made a hex bored wall gun for Indian service in 1866 which had a removable breechblock. It was mounted on a yoke with pin. Artillerman fired one in a long range match several years ago.

Bob

Hey look what appeared while I was typing.

Offline Cannoneer

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Re: wall-gun question
« Reply #8 on: May 09, 2011, 09:00:24 PM »
Artilleryman,

What is the caliber of your Whitworth?
RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

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Offline oltom

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Re: wall-gun question
« Reply #9 on: May 10, 2011, 03:01:13 AM »


Is this the gun you are talking about?

REAL close!!!...slight differences.....wow.......i'm hooked!
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Offline Artilleryman

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Re: wall-gun question
« Reply #10 on: May 10, 2011, 12:02:59 PM »
Artilleryman,

What is the caliber of your Whitworth?

I was told that it is .75 caliber.  I have used .69 caliber rounds in it, and they seem to fit.  I think it depends on how you measure the bore, across the flats or across the "grooves".
Norm Gibson, 1st SC Vol., ACWSA

Offline keith44

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Re: wall-gun question
« Reply #11 on: May 10, 2011, 04:20:53 PM »
Rate of twist needed to stabalize a round ball depends on the diameter of the ball, and the desired velocity of the projectile upon exiting the muzzle.  What you are really after is revolutions per second of flight time.  One inch diameter and an assumed 1,300 fps velocity (max) (black powder load) I'd say around 1 turn to 100 inches or slower
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Offline guardsgunner

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Re: wall-gun question
« Reply #12 on: May 10, 2011, 04:39:01 PM »
Though Norm shot .69's , the gun was designed to shoot a projectile. Molds for most of the non standard calibers are hard to come by.

Offline Cannoneer

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Re: wall-gun question
« Reply #13 on: May 11, 2011, 08:44:35 PM »
Thanks, Artilleryman and guardsgunner; I'd read of the famed accuracy of the Whitworth .45 caliber Sharpshooter that some CSA snipers used in the CW, but I knew nothing about Whitworth's larger bore breech loader.
RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

The one thing that you can almost always rely on research leading to, is more research.

Offline flagman1776

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Re: wall-gun question
« Reply #14 on: July 05, 2011, 02:37:45 PM »
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Offline KABAR2

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Re: wall-gun question
« Reply #15 on: July 06, 2011, 06:15:55 AM »
They came both rifled and smooth bore I owned two originals one a 1" smooth bore full octagon swamped barrel English, the other Germaninc 75 caliber rifled & looked like a Yeager on steroids.There is a place that produces a kit but it usually takes 6 months to get it.
 
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