The smart phone application
called **ArcCalc** can be used to identify rifled artillery from measurements
of the impressed rifling found on projectile fragments. Rifled artillery from
both sides possessed sabots that took the rifling of the rifle barrel.
Typically, the sabots were made of a soft metal (lead, brass or copper). Wrought
iron and, even wood, hemp and papier-mâché were also used.

Android and Apple **
ArcCalc** apps are available from Play Store (for Android) and the Aps Store
(for IOS). Both applications are called **ArcCalc** and are identical, even
though the authors are different.

**ArcCalc**
was first introduced in my webpage article: *“Quick Way to Estimating the
Diameter of Spherical and Elongate Projectile Fragments”.*

Using ArcCalc, the **arc length**
(AL in the
figure below below) can be determined for a single pair of impressed rifling
lands and grooves (L and G)) found along the sabot of the projectile.

The arc length is found from the
measured **chord length** (CL) and the radius of the projectile. Using these
results the total number of lands and groove rifling sets that can be fit abound
the sabot can be estimated. This can then be used to identify the firing rifle.

__
The arc length of a
single set of rifling lands and grooves will always be larger than the chord
length and is a better estimate of the number of total land and groove sets
around the circumference of the sabot. __

The total number of land and groove sets can be used to identify the firing rifle.

*
Sabot of typical 3
lands and groves rifling on the end of a rifled projectile. Using ArcCalc, the
Arc Length (AL) of a single pair of rifling lands and grooves found on the
projectile’s sabot can be found from its measured Chord length (CL) and the
radius of the projectile. Using these results the total number of lands and
groove rifling sets can be estimated. This can then be used to identify the
firing rifle.*

**
Finding the total
number of Land and Groove sets:**

C = Circumference of the sabot of the projectile and ϖ = 3.14159

D = Diameter or caliber of the projectile

N = the total number of Land and Groove sets around the circumference

(L+G) = the arc length of a single Land + Groove set

** Note**:
The value of L+G is found from ArcCalc with the cord length measured by caliper
of L+G.

C = ϖD = N(L+G)

Solving for N (total number of L+G sets around sabot)

N = ϖD/(L+G)

The value of N then can be used to identify the firing cannon.

**
An
Interesting Example**

**
**Two
Confederate Read pattern shell bases were found on the Federal side of an 1864
battlefield in Virginia. One of the bases showed some damage to its sabot on
hitting the ground but still showed a single land and groove set from the
rifling of its firing cannon.

**
Typical Confederate Read pattern
projectile from a Virginia battlefield. Note the lathe dimple found in the
center of the projectile base. **

**
Read Projectile direct caliper
diameter measure of 2.96 inches at bourrelet. Projectile radius (used in ArcCalc)
=2.96/2=1.48 inches**

The chord length of a single let of rifling lands and grooves set was measured with a caliper and found to be 1.27 inches. The cord length and radius of the projectile (half of its diameter) were input into the ArcCalc application and the arc length of the set was calculated to be 1.313 inches.

The L+G chord length value (1.27) and the measured radius (2.96/2) can be used in the above equations to obtain the estimated total number of land and groove sets (N) that could be fit abound the circumference of the sabot using the calculated L+G arc length (1.313):

N = ϖD/(L+G)

N = (3.14159(2.96))/1.313 = 7.08 sets

**
Interestingly:**
The Confederate 3-inch Rifle had possible rifling patterns of 5, 6, or 12
lands and grooves sets.

The Federal 3-inch Ordnance Rifle had a single rifling of 7 lands and grooves.

The Confederate Read
projectile was fired from a __captured Federal 3-inch Ordnance Rifle.__

*
Using the chord
length solution will always give a better estimate of the total number of
sets than using the arc length.*

Artillery projectile expert Peter George has suggested that the typical “windage” of a projectile in a rifle bore is 0.1 to 0.04 inches less than the bore itself. This allows the projectile to move freely in the bore.

Thus, from the example above the rifle bore was 3 inches, the estimated projectile diameter (“windage diameter”) would be in the range 2.90 to 2.96 inches. These would yield an ArcCalc arc length range of 1.302 to 1.328 inches.

In our example the calculated arc length was 1.313 lies within this range. If one compares the arc length ranges from the chart below over all rifles in the 2.9 to 3.3-inch bore range, the only rifle that fits is the 3-inch Federal Ordnance Rifle.

**
**

**
The Method**

Use the direct caliber method
(as above) or one of the methods from the website article (*“Quick Way to Estimating the Diameter of
Spherical and Elongate Projectile Fragments”.) *
to determine the
diameter of the projectile fragment.

Input the radius (measured diameter value/2) and the estimate of the chord length of a single land and groove set on the projectile fragment into the ArcCalc application. This should produce the arc length of the land and groove set.

Compare this value to the arc length ranges ("windage diameter range") in the chart below for all bore values near the measured projectile diameter. The firing rifle identification and the total number of land and groove sets (N) are found on the same row of the chart.

**
Author Note:**
The above article is based upon discussions with Civil War artillery
expert Peter George. I am deeply indebted to him for these discussions
and the sharing of his knowledge.

__
Good Additional
Readings:__

** **

Dean S. Thomas, “*Cannons:
An Introduction to Civil War Artillery*”; 1985; (ISBN 9780939631032); 72
pp.

Dickey, Thomas S. &
George, Peter C., “*Field Artillery Projectiles of the American Civil War*”;
1993; Arsenal Publications; (ISBN 0960902201); 552 pp.

Jack W. Melton &
Lawrence E. Pawl, *“Guide to Civil War Artillery Projectiles”*;
1996;Kennesaw Mountain Press; (ISBN 0-9635861-1-4); 96 pp.

John C. Hazlett,
Edwin Olmstead, & M. Hume Parks, *“Field Artillery Weapons of the Civil
War”*; Revised Edition; 1988; University of Chicago Press; (ISBN
0-252-07210-3); 322 pp.

Steven Roberts, *
“Captain Alexander Blakely RA”*; 2012,
www.scribd.com/document/97550420,
72 pp.

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