20-pdr or 3.67-inch Army Parrott Rifle

Anyone who has studied the artillery used at Gettysburg knows the heaviest rifled guns on the field at the battle were 20-pdr Parrott rifles.  While  heavier weapons in the siege classification saw some use with the field armies, the 20-pdr was for all purposes the “heavy iron” of the field artillery during the Civil War.

5th New York Light Battery - Cemetery Hill
5th New York Light Battery – Cemetery Hill

Like its siblings, the 10-pdr and 30-pdr Parrotts, gun-founder Robert Parker Parrott designed the 20-pdr using composite construction.  By placing a wrought iron band around the breech of a cast iron gun tube, Parrott’s West Point Foundry produced an affordable weapon which reached mass production faster than contemporary rifled guns.  Parrott’s process went beyond just sliding a reinforcing band on the gun as other contemporaries had done.  His technique involved specific a method to construct the band, affix the band to the tube, and to cool the piece.  The entire process is best discussed in a separate post, but for those interested in the details, the patent itself offers ample explanation.

“Patented 1861” Mark on Band

One might think Parrott evolved his weapons in order of caliber.  Not the case.  While 10-pdr and 30-pdr Parrotts saw action in the early battles in Virginia, 20-pdr production did not start until the summer of 1861.  (And some of those early orders were from Southern states!)  Federal ordnance officers accepted the first lots in the summer of that year.  Some were around by the time of First Bull Run, although the dates indicate either a short acceptance test, or lack thereof.  20-pdrs were in action at the battle of Balls Bluff providing support from the Maryland side of the river near Edwards Ferry.  Production continued until the fall of 1864 with over 330 examples delivered for Army or state contracts.  West Point Foundry delivered a similar quantity to fill Navy contracts during the course of the war.

In terms of construction, the 20-pdr was a scaled down 30-pdr.  On the 20-pdr, the characteristic band was 16.5 inches long and 1.5 inches thick (compared to 13 inches by 1.19 inches for the 10-pdr; 19 inches by 2 inches for the 30-pdr).    The bore measured 3.67 inches across the flats.  That caliber corresponded directly with the 6-pdr field gun then in service.   The 20-pdr had five groove increasing pitch rifling, designed to use Parrott’s patent projectiles.

Muzzle of 20-pdr #205

Overall the finished gun tube measured nearly 90 inches long, with weights varying between 1650 and 1800 pounds.  On the exterior, the 20-pdr had no muzzle swell.  The gun narrowed sharply just in behind the trunnions.  This gave the 20-pdr a “swelled” appearance between the trunnions and reinforcing band.

“Swell” between Band and Trunnions

A socket for the rear sight extended from the back of the breech band.

Breech Band and Rear Sight Socket

A tapped hole on the right rimbase supported the blade front sight.

Right Trunnion and Hole for Sight

Trunnions measured 4.62 inches in diameter and 3.5 inches long.  Because of such, the 20-pdr Parrott used a modified 32-pdr Field Howitzer carriage.  Dressed out for service, the gun on its carriage with limber weighed in excess of 4400 pounds.  This rated the weapon among the heaviest designated for field service, requiring an eight horse team.

“20 Pdr” on Left Trunnion

Range tables from the manuals of the day cited a maximum range of 4400 yards at a 15 degree elevation for an 18 pound shell.  The more realistic field range was 2200 yards at 6 degrees of elevation, given line of sight and carriage elevation limits.  In other words, not much greater than a 3-inch rifle (Ordnance or Parrott) firing a projectile half that weight.

Once again I call the reader’s attention to the relationship between the weight of a gun in action, ballistic performance, and ammunition supply.  The 20-pdr Parrott required four additional horses (two more for the gun/limber and two more for the caisson), than a 3-inch or 10-pdr rifle.  It offered only a marginal range increase.  Although offering a heavier projectile, a 20-pdr brought only 75 ready rounds to the battle (25 on the limber and 50 with the caisson).  Thus a 20-pdr could stand on the firing line roughly half the duration of a lighter 3-inch rifle, which brought 150 rounds to the fight.

Regarding the usefulness of the 20-pdr, Henry L. Abbot, while detailing siege operations around Richmond, wrote, “The 20-pounder Parrott (calibre 3.67 inches) proved to be too small to give the precision of fire demanded of a siege gun, and to be too heavy for convenient use as a field gun.”  Abbot went on to complain about the performance of projectiles.  Because of these and other factors, the gunners were less enthusiastic about the 20-pdr than other of Parrott’s products.

20-pdr in Evergreen Cemetery

Unlike the lighter 10-pdr/3-inch Parrott, the 20-pdr did not undergo a model change in the middle of the war.   Aside from differences regarding stampings, the only noteworthy variation among the 20-pdrs is the cascabel.  The standard Army pieces featured a somewhat flattened knob.  And standard Navy production had breeching jaws and a block, resembling a ring when viewed from the side, to support breeching tackle for shipboard use.  However with demand outstripping production, some Army models were supplied to the Navy.  The Navy modified those batches by adding a “U” shapped bracket attached with an iron bolt, fixed to a machined slot in the cascabel.  Two examples weapons so modified are at Gettysburg representing Confederate batteries on Seminary Ridge.  Unfortunately at this time both are undergoing maintenance, so once again I (regretfully) go to the 35mm photos in the shoebox.

20-pdr Army with Navy Breeching Loop

Two other Federal 20-pdr Parrotts at Gettysburg accurately represent Captain Elijah Taft’s 5th New York Light Artillery Battery, looking from Evergreen Cemetery north over the National Cemetery.  However, that battery’s other position marked by War Department tablets features 20-pdr Parrotts of Confederate manufacture.  And that is my queue to start writing a follow-up post….

Taft’s Other Position

Two more 20-pdr Parrotts guard the Vigo County Civil War memorial in Terre Haute, Indiana.    And another 20-pdr stands upright in the Antietam National Cemetery.  All told 56 of the Army 20-pdr Parrotts have survived to see the sesquicentennial.

20-pdr in Antietam National Cemetery

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