Pratt & Whitney purchased the manufacturing rights to Gardner patent of 1876, and then steadily improved the design. After the split with Gardner, a senior engineer of Pratt & Whitney, Edward G. Parkhurst, made substantial improvements to the locks, feed mechanisms, and barrel cooling arrangements. The 'Improved' Gardner gun, using Parkhurst's patents, was marketed by Pratt & Whitney from 1881. The U.S. Government, however, was wedded to the Gatling and very few Gardners were bought for the U.S. Army or Navy.
2 barrel Improved Gardner gun model 1883 to Edward Parkhurst's 1880 design. Note water cooled enclosed barrels, spent cartridges drop through the base of the casing and ammunition feeder has two columns of cartridges.
If you are unable to view this Quicktime movie, click here to view the animation on YouTube
The Pratt & Whitney Gardner Gun
Although William Gardner made his first prototypes in wood and metal, he did not have the resources to manufacture his gun, and he sold the manufacturing rights to Francis Pratt and Amos Whitney in 1875. Pratt & Whitney developed the gun to meet military requirements and demonstrated it to the U.S. Navy Ordnance Board in November 1875. Improvements were needed, and Pratt & Whitney had their Assistant Plant Superintendent, Edward G. Parkhurst make improvements to the gun’s design over the following three years [Gn6]. Pratt & Whitney demonstrated an enclosed 2-barrel gun to the U.S. Navy in June 1879. The gun worked smoothly during the trials with no misfires and only 6 failures to extract when firing 10,000 rounds. The total time for actually firing 10,000 rounds was 27 minutes 36 seconds [Gn5]. This gun, which was also exhibited at the 1878 Paris Exposition, used substantially the same mechanism patented by William Gardner in 1876. Unfortunately, the United States Services were content with their Gatling guns, and no purchases were forthcoming.
Edward Parkhurst then made significant engineering and design changes, which resulted in an ‘improved’ Gardner Gun. Parkhurst submitted a patent for his improvements in the gun mechanism in January 1880 and this was granted on June 15, 1880 [Gn9]. Two other patents were granted to Edward Parkhurst that year, an ammunition feeder with two columns of cartridges that could be reloaded while the gun was firing, and a water filled enclosure around the barrels to keep them cooled when firing at high rates.
The animation shows the operation of the ‘improved’ Gardner gun designed by Edward Parkhurst in 1880. Despite the excellence of the mechanism, and it being significantly lighter that Gatling guns, Pratt and Whitney were only able to sell 21 guns to the U.S Army over the next 20 years. They did, however, manufacture 250 for the Italian Government, and sold manufacturing rights for a further 200. [Gn6]
Naming the Parts.
The Parkhurst Gardner design follows the Gardner gun principle with two barrels arranged horizontally and reciprocating locks that load and fire alternately. The locks are driven backward and forward by cams on a crankshaft turned by hand. However, the firing locks and the cartridge feed mechanisms are substantially different.
Feeder plate slides sideways to regulate supply of fresh cartridges (Rollover)
As lock moves to the rear, the retractor eases spent cartridge out of breech (Rollover)
Ejector arm kicks spent cartridge out of the cartridge carrier (Rollover)
With the lever to safe, the firing bolt cannot reach the cartridge when released (Rollover)
Rocking arm compresses spring just before firing. During extraction, firing bolt is pushed back to be held by hooked lever (Rollover)
The firing mechanism is held entirely within the body of the lock. The firing bolt has a fixed collar, and behind this a spiral spring. The spring is compressed by sleeve which can be moved along the bolt axis by a rocking lever. The rocking lever head is cut with teeth which engage with a rack on the underside of the sleeve.
As the lock is drawn back, the rocking arm rides over a fixed incline and pushes the sleeve and bolt backwards. When fully back, the bolt head rides over the hook of a hooked lever and is held there. The lock then travels forwards, and the base of the rocking arm catches on a sliding block. This causes the rocking lever to push the sleeve forwards, so compressing the firing spring. The head of the bolt is held back by the hooked lever until the lock has been pushed fully forward, and the cartridge is fully home in the breech. The cam then trips the hooked lever, allowing the bolt to fly forwards and ignite the cartridge.
The Safe-Fire Lever
The firing spring is only compressed when the rocking lever rides up against the sliding block. To make the gun safe – so that no further discharges will occur, the safe-fire lever is turned and this moves the sliding block forwards. Now the rocking lever is not rotated, the firing spring is not compressed, and when the hooked lever releases the bolt, it cannot move far enough to reach the cartridge. The crank handle can continue to turn, and cartridges will continue to be loaded, but they will not fire.
The gun needs a reliable way to extract spent cartridges after firing. Parkhurst’s design has two components – a spring extractor fixed to the lock that hooks over the rim of the cartridge so that it can be pulled out of the breech, and a Retractor. The retractor is a curved lever at the front of cartridge carrier. When the lock is fully forward, the arm of the retractor lever slots into a groove cut in the side of the lock. As the lock moves backwards after firing, the retractor arm is pivoted out of the slot, and the hook end forces the cartridge back a little way. This is important, as the metallic cartridge will have been expanded by the explosion of the propellant, and needs to be freed so that the spring extractor can pull it out. The retractor has a second purpose – it ensures that the spring extractor has ridden over the cartridge head during the loading movement. If the spring extractor has not clipped over the cartridge rim, the cartridge will reach the retractor’s hooked arm and be held there until the lock is far enough forward for the retractor’s long arm to enter the slot on the lock, and to do this, the spring extractor must be hooked over the cartridge rim.
The Cartridge Carrier
The cartridge carrier has two troughs lined up behind the barrels. A slot is cut in each trough which is wide enough for most of its length to allow the body of a cartridge to drop through, but is too narrow to pass the cartridge rim. Therefore when a fresh cartridge is dropped in by the feed plate, it cannot fall through. The rear of the slot is cut wider. When the spent cartridge is extracted, the lock pulls the cartridge further back than its loading position, and the rim can now pass through the enlarged slot.
The Ejecting Lever
At high rates of fire, it is not sufficient to rely on gravity to clear a spent cartridge from the trough. Parkhurst’s design, therefore, includes an Ejecting Lever with each lock. When the lock is almost fully to the rear, a dog on the lock rides on the short arm of the ejecting lever, causing the long end to swing inwards sharply. The end of the arm strikes the spent cartridge, forcing it down and out through the slot in the cartridge carrier. The ejecting lever is positioned so that it always hits the cartridge above its centre-line to ensure the motion is downwards. The end of the long arm of the ejecting lever is now placed so that it will prevent a fresh cartridge from sliding backwards far enough to drop through the slot.
The Feed Plate
The feed plate slides sideways to regulate the flow of cartridges into the cartridge carrier troughs. Its sideways movements are caused by a lever which is pushed one way and back by the vertical arms of the locks, and operates just each lock reaches its forward-most position. The feed plate moves between the cartridge feeder guides (forming part of the cover), and the cartridge carrier, so that one cartridge at a time from each column can drop into the feed plate
The feed plate is cut with slanting slots wide enough to pass a cartridge. As the feed plate moves each way, cartridges are forced downwards by the incline, rather than drop under gravity to give a more positive feed.
Pratt & Whitney's Gardner gun demonstrated to the U.S. Navy in 1879 fired a burst of 2,000 rounds with an average of 380 rounds a minute. The barrels became so hot after this that they had to be cooled by pouring water through them. In the ‘improved’ Gardner design, Parkhurst patented a sleeve that fitted around the barrels and could be filled with water. In his patent, he shows a filler cap as well as a drain plate, but modern reproductions dispense with the filler cap and simply leave a hole in the top of the cover (if the gun were to be used in a naval situation, for example in the fighting tops, then without the filler cap, all the water would run out when firing down onto the enemy’s decks).
Improved Cartridge Feeders
Parkhurst original patent of June 1880 specified a cartridge feeder case that contained a number of rounds. It was loaded externally and slotted into the gun cover, and in doing so spring-loaded arms in the case released the cartridges to fall onto the feeder plate. When the case was removed, the arms sprang back to hold any remaining cartridges. The case would have to be replaced by a charged case when empty.
This was clearly not efficient, and Parkhurst patented in 1880 a feeder design that allowed the rims of cartridges pre-loaded into wooden blocks to be slid into grooves in the feeder. Parkhurst’s design had a sliding cover that held the cartridges in place until they were loaded. The width of the blocks holding the cartridges was determined by the distance between the barrels, and therefore was not the most efficient use of magazine space. Later patents produced more cartridge block that made better use of space, and even could use ammunition straight from the cardboard packaging straight from the manufacturer.
Model of 2-barrel 'improved' Gardner Gun, to the 1880 designs and patents of Edward Parkhurst.
Reproduction of the 1885 "Improved" Gardner Battery Gun, manufactured by Special Interest Arms, Gardnerville, NV.
My thanks to Special Interest Arms, who manufacture reproduction Parkhurst design Gardner guns, for permission to use their photographs.
To view an excellent YouTube movie showing the Parkhurst design of Gardner gun in operation, Click here.
Gn5. The Machine Gun, Volume I, Lieutenant Colonel George M. Chinn, USMC, 1951
Gn6. Rifle Calibre Artillery: The Gardner Battery Gun, James W. Alley Jr. American Society of Arms Collectors Bulletin No 89.
Gn9. U.S. Patent No. 228,777 dated June 15, 1880, Machine-Gun, granted to Edward G Parkhurst and the Pratt & Whitney company