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Ballistic Coefficient for Cannon

This is a discussion on Ballistic Coefficient for Cannon within the Military History forums, part of the Armed Services category; Originally Posted by 2336USMC What was your elevation for that group? Do you reference your elevation to a bubble level of some sort, or a ...


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Old March 8th, 2017, 06:37 PM   #31
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What was your elevation for that group? Do you reference your elevation to a bubble level of some sort, or a plumb bob?
SIR: One of the best sighting units used during that time was a simple Pendulum Hause, please excuse my spelling, this unit would either sit on the left side of the barrel on the likes of a Parrot, or on the center on the 3" in ordnance rifle. This sighting piece was much like the sights on our 1903 ladder sights. There was a peep hole and graduations for yardage. The sight was allowed to sway from side to side on a set of pins, this allowed the sight to compensate for uneven ground, thus keeping from throwing off sight picture. They also used a Quadrant for estimating elevation.

Now lets be realistic those men did not in my humble opinion take the time to do all of this sighting.. They would roll up with the gun un-limber and take an estimation of the distant, select the proper round (ie) case shot, canister, or solid shot for counter battery fire, and fire, and then adjust. They would expend the limber of the shots and then retire with the gun!!!
Badger5th, sir I do not underestimate those charts, I, from my limited experience firing on the farm have fond that the modern powders and shells have quite a difference in yardage and flight pattern.... We in my battery are now trying a different shell following the hodkiss pattern . We have a gentlemen in Pa. who built our gun making our rounds, and you are quite right, $80.00 to $100.00 a shot can be a little taxing to us Southern Boys!!!

Yours for the Cause!!!

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Old March 8th, 2017, 06:47 PM   #32
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What was your elevation for that group? Do you reference your elevation to a bubble level of some sort, or a plumb bob?
Badger5th sir I did not see your post with the pictures on the sighting units, well done sir, you are quite a bit better than I'am with the computer, ha ha

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Old March 8th, 2017, 07:21 PM   #33
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SIR: One of the best sighting units used during that time was a simple Pendulum Hause, please excuse my spelling, this unit would either sit on the left side of the barrel on the likes of a Parrot, or on the center on the 3" in ordnance rifle. This sighting piece was much like the sights on our 1903 ladder sights. There was a peep hole and graduations for yardage. The sight was allowed to sway from side to side on a set of pins, this allowed the sight to compensate for uneven ground, thus keeping from throwing off sight picture. They also used a Quadrant for estimating elevation.

Now lets be realistic those men did not in my humble opinion take the time to do all of this sighting.. They would roll up with the gun un-limber and take an estimation of the distant, select the proper round (ie) case shot, canister, or solid shot for counter battery fire, and fire, and then adjust. They would expend the limber of the shots and then retire with the gun!!!
Badger5th, sir I do not underestimate those charts, I, from my limited experience firing on the farm have fond that the modern powders and shells have quite a difference in yardage and flight pattern.... We in my battery are now trying a different shell following the hodkiss pattern . We have a gentlemen in Pa. who built our gun making our rounds, and you are quite right, $80.00 to $100.00 a shot can be a little taxing to us Southern Boys!!!

Yours for the Cause!!!
Just curious. Was it Jeff Stafford who made your gun? Jeff is the only guy I am aware of in PA who does CW ordnance carriage work. Jeff built two of our three limbers and most of the wheels that are currently in service on our equipment.

Our unit owns two 3-inch ordnance rifles. Both tubes South Bend cast steel with a Paulson rifled liner. One carriage we built ourselves, the second carriage is a Paulson carriage.

FYI Gen Henry Hunt, who was commander of the federal arty reserve, issued a general order that gun crews were not to exceed one round per minute unless the urgency of the situation required a greater rate of fire. He urged even slower rates of fire for long distance shooting so the gunners would aim properly.

Regards,
Badger

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Old March 8th, 2017, 07:43 PM   #34
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OK...

Your BC is about 2. Sierra Infinity Ballistics won't accept a BC higher than 2, but 2 is very very close.

Using a BC of 2, muzzle velocity 1250fps, zero range 830 yards (projos struck ground at about 865, but would have been level with muzzle at about 830) here's what we get:

Projo will drop an additional 85" between 830 and 900, so add 9 MOA elevation (.15 degree) to hit muzzle level at 900. Add to that for height of bullseye, i.e. if the bullseye is 36" higher than muzzle level, add another 4 MOA to hit center.

Drop from 830 to 1000 is 231 inches, so add 23 MOA (.38 degree) to hit muzzle level at 1000, again add more if the bullseye is higher than the muzzle.

So it looks like your 900 yard zero is about 1.65 degrees, 1000 yards zero is 1.88 degrees.

Fun facts:

Remaining velocity at 1000 yards: 1071 fps
Max ordinate: 218" (18.2 feet) above line of sight at 425 yards (useful for firing over the heads of troops)
Max range: 8383 yards at elevation of 39 degrees
If you fired it straight up, it would reach max height of 14,444 feet and take 27.98 seconds to get there. Plenty of time to move out of the way before it comes back down.

EDIT: Note for those who will want to argue G1 BCs, this solution was backwards engineered from the actual firing data provided by Badger5th. It is based on reality. Given the known MV of 1250, the known launch angle of 1.5 degree (90MOA), and the known point of impact, there is only one G1 BC that accounts for that: 2 (or very very close.) Note also, as what is known as a "seat of the pants check," IOW does the data make common sense, the solution from Sierra fits perfectly with what we know- they need a little more than 1.5 degrees, and the Sierra solution shows that, plus it falls right in between the projo manufacturer's suggestion and the Red Book solution, so it makes sense and passes the seat of the pants test.

I'm guessing if the Red Book says 2 degrees for 900, the original cast iron projo and black powder load must have had a lower MV. The 10 pound projo with Goex, at 1250fps, is shooting a little bit flatter (faster) than the original Civil War load. .35 degrees flatter to be exact. (Oops, no smoking next to the black powder...)

Thanks from Badger5th

Last edited by 2336USMC; March 8th, 2017 at 08:29 PM.
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Old March 9th, 2017, 02:58 PM   #35
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Quote:
Originally Posted by 2336USMC View Post
OK...

Your BC is about 2. Sierra Infinity Ballistics won't accept a BC higher than 2, but 2 is very very close.

Using a BC of 2, muzzle velocity 1250fps, zero range 830 yards (projos struck ground at about 865, but would have been level with muzzle at about 830) here's what we get:

Projo will drop an additional 85" between 830 and 900, so add 9 MOA elevation (.15 degree) to hit muzzle level at 900. Add to that for height of bullseye, i.e. if the bullseye is 36" higher than muzzle level, add another 4 MOA to hit center.

Drop from 830 to 1000 is 231 inches, so add 23 MOA (.38 degree) to hit muzzle level at 1000, again add more if the bullseye is higher than the muzzle.

So it looks like your 900 yard zero is about 1.65 degrees, 1000 yards zero is 1.88 degrees.

Fun facts:

Remaining velocity at 1000 yards: 1071 fps
Max ordinate: 218" (18.2 feet) above line of sight at 425 yards (useful for firing over the heads of troops)
Max range: 8383 yards at elevation of 39 degrees
If you fired it straight up, it would reach max height of 14,444 feet and take 27.98 seconds to get there. Plenty of time to move out of the way before it comes back down.

EDIT: Note for those who will want to argue G1 BCs, this solution was backwards engineered from the actual firing data provided by Badger5th. It is based on reality. Given the known MV of 1250, the known launch angle of 1.5 degree (90MOA), and the known point of impact, there is only one G1 BC that accounts for that: 2 (or very very close.) Note also, as what is known as a "seat of the pants check," IOW does the data make common sense, the solution from Sierra fits perfectly with what we know- they need a little more than 1.5 degrees, and the Sierra solution shows that, plus it falls right in between the projo manufacturer's suggestion and the Red Book solution, so it makes sense and passes the seat of the pants test.

I'm guessing if the Red Book says 2 degrees for 900, the original cast iron projo and black powder load must have had a lower MV. The 10 pound projo with Goex, at 1250fps, is shooting a little bit flatter (faster) than the original Civil War load. .35 degrees flatter to be exact. (Oops, no smoking next to the black powder...)
I'm getting a BC of .937

And, I am getting near the same elevation as you:

900 yard zero, 1.8 degrees
1000 yard zero - 2.1 degrees

The max ordinate is pretty much the same as yours, too

My BC is based on the fact that the bolt is almost the exact same shape as a flat nose 500 grain .450 projectile. Ijust backed out the form factor using:

B.C. = SD x i

with

SD = the projectile weigh (lbs) divided the square of the diameter (in)
i = form factor

then applied it to the new sectional density of the larger projectile.

The calculator I was using, with the projectile weight 71,750 grains.



Either way, it looks like your probably "on paper" at 900 yards somewhere around 1-5/8 to 1-7/8 degrees elevation.

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Old March 9th, 2017, 03:26 PM   #36
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I started from the same place, I looked up the BCs of a number of long flat point bullets with similar shape in 45 and 50 cal. BC of about .29 seemed pretty typical for those, so I started with that but .29 was obviously way too low for the 10 pound data, to get 830 yd zero at 1250 fps required a much higher launch angle than 1.5 degrees... so I just kept inputting higher BC values, everything else constant, until the launch angle came down to 1.5 degrees, which was with a BC right at 2.00.

Sierra doesn't give launch angle of elevation directly, but it does give projectile drop below bore line and projectile path. 2.00BC at 1250 FPS, 830 yd zero, shows 11" drop below bore line and 79" above line of sight at 100 yds. 79+11 = 90 inches, roughly 90 MOA at 100 yds, therefore launch angle of 1.5 degrees, IOW if it was a laser beam instead of a projo the bore is pointed 90 inches above line of sight at 100 yds.

We could get a more precise solution if we knew the environmental conditions at the time the recorded group was fired, the expected conditions for the shoot in NY in June, and did the math for exact MOA instead of shooter's MOA, but I'll bet my data is close enough for a cannon, or ordnance rifle.

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Old March 9th, 2017, 03:44 PM   #37
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I ran it using your BC of .937 and Sierra predicts that would have struck ground at 790 yards.

Oh, I also guessed that the muzzle of the gun is 3 feet above the ground, and the front sight is 6" above bore center. We would need those numbers also, but that should be close.

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Old March 9th, 2017, 04:11 PM   #38
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Originally Posted by 2336USMC View Post
I started from the same place, I looked up the BCs of a number of long flat point bullets with similar shape in 45 and 50 cal. BC of about .29 seemed pretty typical for those, so I started with that but .29 was obviously way too low for the 10 pound data, to get 830 yd zero at 1250 fps required a much higher launch angle than 1.5 degrees... so I just kept inputting higher BC values, everything else constant, until the launch angle came down to 1.5 degrees, which was with a BC right at 2.00.

Sierra doesn't give launch angle of elevation directly, but it does give projectile drop below bore line and projectile path. 2.00BC at 1250 FPS, 830 yd zero, shows 11" drop below bore line and 79" above line of sight at 100 yds. 79+11 = 90 inches, roughly 90 MOA at 100 yds, therefore launch angle of 1.5 degrees, IOW if it was a laser beam instead of a projo the bore is pointed 90 inches above line of sight at 100 yds.

We could get a more precise solution if we knew the environmental conditions at the time the recorded group was fired, the expected conditions for the shoot in NY in June, and did the math for exact MOA instead of shooter's MOA, but I'll bet my data is close enough for a cannon, or ordnance rifle.
Well, the BC is a combination of the form factor (shape) and the sectional density. The sectional density of a 10-1/4 pound (72,000 grain), three inch shell is going to be a wee bit higher than a .071 pound, .45 inch projectile.

I dunno, I am getting almost the exact same numbers as you are, but I certainly think we have dialed in the elevation.

I have been assuming a 3 foot trunnion height as well.

For a 10 mph 90 degree cross wind, what kind of windage error are you getting at 900 yards? I'm getting about 65 inches.

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Old March 9th, 2017, 04:26 PM   #39
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Are sure you're using a 71,750 grain projectile?

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Old March 9th, 2017, 04:39 PM   #40
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Originally Posted by 2336USMC View Post

We could get a more precise solution if we knew the environmental conditions at the time the recorded group was fired, the expected conditions for the shoot in NY in June, and did the math for exact MOA instead of shooter's MOA, but I'll bet my data is close enough for a cannon, or ordnance rifle.
The day we shot at 900 yards the temp was about 80 degrees with light and variable winds.

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Old March 9th, 2017, 04:41 PM   #41
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I have been assuming a 3 foot trunnion height as well.
It's right around 36-42 inches.

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Old March 9th, 2017, 04:43 PM   #42
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I ran it using your BC of .937 and Sierra predicts that would have struck ground at 790 yards.

Oh, I also guessed that the muzzle of the gun is 3 feet above the ground, and the front sight is 6" above bore center. We would need those numbers also, but that should be close.
Muzzle would be approx 42-46 inches above grade at 1.5 degrees elevation. Front sight is closer to 5 inches above axis of bore.

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Old March 9th, 2017, 04:54 PM   #43
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Originally Posted by 2336USMC View Post
I started from the same place, I looked up the BCs of a number of long flat point bullets with similar shape in 45 and 50 cal. BC of about .29 seemed pretty typical for those, so I started with that but .29 was obviously way too low for the 10 pound data, to get 830 yd zero at 1250 fps required a much higher launch angle than 1.5 degrees... so I just kept inputting higher BC values, everything else constant, until the launch angle came down to 1.5 degrees, which was with a BC right at 2.00.

Sierra doesn't give launch angle of elevation directly, but it does give projectile drop below bore line and projectile path. 2.00BC at 1250 FPS, 830 yd zero, shows 11" drop below bore line and 79" above line of sight at 100 yds. 79+11 = 90 inches, roughly 90 MOA at 100 yds, therefore launch angle of 1.5 degrees, IOW if it was a laser beam instead of a projo the bore is pointed 90 inches above line of sight at 100 yds.

We could get a more precise solution if we knew the environmental conditions at the time the recorded group was fired, the expected conditions for the shoot in NY in June, and did the math for exact MOA instead of shooter's MOA, but I'll bet my data is close enough for a cannon, or ordnance rifle.
Gentleman, you and lysander are such a great asset to the forum!!! I will apply your settings to my gun in the near future and see what it does at 900 and 1000 yards!!
Badger5th I misspoke earlier when I said that the sighting was like the the 1903 ladder sight set in yardage, you and the rest are quite right that it is set in elevation not yardage!!! I guess craft is setting in ( can't remember ) now I did leave the rest out, don't need to be sent to the banned camp!!!!

I also do not like to use folks name on this forum without their permission, but you could be right about my builder. He makes one hell of a gun and carriage. When I feel confident in my abilities I shall try to shoot at one of the competitions...

Yours for the Cause!!!


Last edited by XXIV Corps; March 9th, 2017 at 08:30 PM. Reason: ROE #11, Inappropriate Language, we want this community to be family friendly for all generations.
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Old March 9th, 2017, 06:03 PM   #44
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What Jaycosta said on page one. Get a labradar and quickload. Especially labradar. You may set a record for distance reading. If they can pickup a boat tail on a .308 imagine how far they can read your slug.

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Old March 10th, 2017, 07:09 AM   #45
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What Jaycosta said on page one. Get a labradar and quickload. Especially labradar. You may set a record for distance reading. If they can pickup a boat tail on a .308 imagine how far they can read your slug.
We can see a 3-inch projectile during the whole flight with 10x binoculars. They're BIG chunks of metal.

Regards,
Badger

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