Comparing the Big Guns: Rodman vs. Confederate Columbiad

Placement of several 10-inch smoothbore guns at Fort Moultrie, South Carolina allow for direct comparison of different types used for seacoast defense during the Civil War era.

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Cannon Row at Fort Moultrie - Two Rodmans, a Columbiad, a Seacoast mortar

For the last few cannon posts, I’ve focused on the Confederate Columbiads.   The example at Fort Moultrie is one of these “cast to a revised pattern” from Tredegar Foundry.  Cast on August 20, 1862, the gun is foundry number 1656.

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Tredegar 10-inch Columbiad #1656

As I’ve stressed in the earlier posts, the Confederate Columbiads retained a cylindrical reinforce while introducing a gradually tapering barrel.  While not exactly the same, the end result is an external form similar to the Rodman guns produced in the North during the war.  Still the “flat” of the reinforce stands in contrast to the curves of the Rodman.

Here’s one of those Rodman guns.  Fort Pitt Foundry, Pittsburgh, Pennsylvania cast this Rodman in the fall of 1863.  It is registry number 156, inspected by Robert H.K. Whitley.  (And as a minor note, I have recorded the registry number of this gun is 158.  But most sources indicate the registry number is 156. So I’ll bow to the preponderance of opinions.)  Notice the “bottle-shaped” exterior form presenting a sweeping curve from the cascabel to the muzzle.

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10-inch Rodman - Fort Pitt #156

The 10-inch Rodman weighed 1,500 to 2,000 pounds more than a Confederate Columbiad of the same caliber.  While Fort Pitt #156 weighed 14,956 pounds, it’s mate #182 from the same foundry weighed 14,980 pounds.

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Muzzle Marks of 10-inch Rodman - Fort Pitt 182

The Tredegar Columbiad’s markings are somewhat weathered but the marks indicate it weighed 13,290 pounds.

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Weight Stamp on Tredegar Columbiad

The Rodmans are longer at 136 inches compared to 123 inches for the Confederate gun.  However both guns have a similar maximum diameter at around 32 inches.  Both taper at about the same rate to the trunnions to a diameter of 26 inches.

Both vendors added sight masses over the trunnions to work with breech face sights.  This was a common arrangement on large-caliber guns.  Just before the war the Army switched to off-center-line sights using a rimbase mounted sight.

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Trunnion of Fort Pitt #182

This view also allows comparison of the trunnions.  The Federal gun has a short, 3.25 inch long trunnion.  The diameter is 10 inches.  The rimbases flair evenly into the barrel.  The Rodmans were designed for use on wrought iron carriages. Now consider the Confederate gun:

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Trunnion of Tredegar #1656

Its trunnion, while the same 10-inch diameter, is nine inches long.  With the exception of some early Confederate Columbiads, the rebel guns used the long trunnions indicating a preference for wooden carriages.

The form of carriage also dictated the elevating system.  The breech of the Confederate Columbiad has angular indentations for its preferred elevation system.

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Breech Face of Tredegar #1656

For the standard wooden carriage (pre-war so such was used by both sides), the elevating mechanism used a “finger” to press against these indentations from below.  The indentations are known as ratchets.  I’ll describe the details of this mechanism in a later post, but will add that the system depended upon the preponderance of weight to the breech end of the gun.

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Breech Face of Fort Pitt #182

On the other hand Rodman guns, after the prototypes and early production batches, had no preponderance; or in other words were balanced evenly on the trunnions.  For elevation, the Rodmans have a set of sockets.  Using a pry bar, the gun crew would elevate the gun by working the pry as a lever trough a cradle.  Again, I’ll compare the two systems in detail later.

The Confederate Columbiad and Rodmans were smoothbores of course.

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Bore of Rodman - Fort Pitt #182

But there were slight differences in the bore bottoms, which are not visible due to the camera perspective.  The Confederate guns used a hemispherical bore bottom, which had come into vogue for heavy guns just before the war.  The Rodmans guns featured an extended hemisphere or semi-elliptical bore bottom.  In the case of the 10-inch Rodman the bore bottom extends 9.75 inches, instead of the hemispherical 5 inches.  This allowed the powder bags to seat better.

Another comparison of the guns, which cannot be captured by photos, is the difference in casting technique.   Rodman guns, as I’ve mentioned in other posts, used a hollow core, water-cooled system.  Tredegar and Bellona cast these Confederate Columbiads using standard casting techniques.

So at this point the reader should be convinced that the term “Confederate Rodman” cannot not be applied to the Tredegar gun and its kin.

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Cannon Row at Fort Moultrie

And as a closing note, I could well continue with another comparison of the guns along cannon row.  Past the two Rodmans (second and third from the camera) is a 10-inch Columbiad Model 1844 which was banded and rifled during the war.

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10-inch Columbiad Model 1844, Banded and Rifled

But I’ll have to save the story of this very interesting gun for another day.

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

7 thoughts on “Comparing the Big Guns: Rodman vs. Confederate Columbiad

  1. Very good work, I am new guide at Fort Monroe Va.and this was most helpful.were there any Cplumbiad to compare to the
    large Rodman seige guns at Fort Monroe?

    1. Barry, there are several surviving Columbiads to compare with Rodmans. At Fort Moultrie is a 10-inch columbiad sitting next to the Rodman guns. But that Columbiad was altered to a banded, rifled gun by Confederates. So a direct comparison is difficult.

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