These cannons are much smaller than the other cannons used here in 1863 such as the Parrotts or Napoleons. These weapons are quickly identifiable as the tubes are black, very smooth, and almost always in terrific shape and represented at the time, some pretty serious weapon technology. The 3-inch ordinance rifle is easily identified by its sleek, tapered barrel and clean lines. SOURCE. Another identifier of the 3-inch ordnance rifle are the stamps found on both trunnions. The trunnions with stamps always read the same: From the guns perspective, the left trunnion reads Patented Dec. 9, 1862 & the right trunnion reads, Phoenix Iron Co.. The trunnions are sometimes devoid of markings. I believe the ones without markings start @ no. 236 and are considered a middle batch. At the time, the patent was still pending or at least that is my understanding. Contract tallies reveal that Registry numbers 236 through 543 were inspected from 20 February through 25 November 1862, before the patent was granted on 9 December 1862. SOURCE
Some other observations of the ordnance rifle is their tubes do not have the breech band seen in the similar looking Parrotts (flared muzzles), which distinguishes the two. The 3-inch carriages and limbers are also always equally pristine. This is an 1861 model but manufactured a few years later in 1864 which means it was not used at Gettysburg. This model was also mass-produced by the Confederates as well, but not nearly as well made as their Union counterparts. The stamps on the outer muzzles of these rifles are almost always legible and often times pristine which allows tracing back the manufacturing origins a snap. I think this is due to the deep incising of the registry inscription/information along the muzzle as compared to other cannons which were much more shallow in their engraving.
The rifle is located on East Cemetery Hill, across the road from the National Cemetery, 78 feet from Baltimore Pike. This site is loaded with weapons and monuments. This Hill is located on the east or left side of Baltimore Pike if traveling south southeast along the road. The gun is located to the right of the mid-section of the hill (if facing the hill with your back to the pike), 13th from the left or 5th from the right, getting close to the end where the monumentation stops. The rifle is pointing to the east northeast. To the immediate left of this rifle is 3-inch rifle no. 922 and to the left of that on the end is no. 7279. Directly in front of this rifle is the 
4th Ohio Infantry Monument. In all, there are seventeen (17) 3-Inch Ordnance Rifles arranged from north to south on East Cemetery Hill. The rifles are protected in earthen lunettes. The gun pits were originally built during the battle, but refurbished and restored by the Gettysburg Memorial Commission (pre-dating the Park Commission & the National Park Service). Photographic evidence shows these pits utilized wood fence rails on the interior. SOURCE The distance between the first and last rifle is 643 feet. The registry numbers moving from north to south are: 3_2, 834, 629, 737, 670, 762, 832, 931, 399, 707, 279, 922, 731, 634, 909, 757, 719. All of these rifles are in terrific shape, and except for the first one, all of the muzzle stamps are deeply incised and very easy to read. 
Parking is available on Baltimore street on the cemetery side at metered spaces running parallel to the road. There always seems to be a space open when I visit. Also, there is a free parking lot on the other side of the rifle, along the Pike located at N 39° 49.328 W 77° 13.792. I visited this monument on the afternoon of Tuesday, August 7, 2012 @ 2:11 P.M. and was at an elevation of 617 feet ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
Through my investigations, I learned the man who made the tablets which accompany the cannons also had a hand in restoring these cannons as well. Gettysburg National Military Park has hundreds of these historic artillery pieces on its field of battle. Their carriages, sights, limbers and on rare occasion (should you find them), the caissons have all been restored. Much of the restorative work came from Major Calvin Gilbert who owned the Gettysburg foundry.
Calvin Gilbert owned a Foundry which bore his name in Gettysburg. This man was responsible for creating all of the cast iron battery tablets. His work did not end there as his foundry created many of the carriages for the historic cannons at Gettysburg. Although almost all of the cannons are from the Civil War, their carriages, sights, limbers, wheels and caissons have been restored at his foundry in the early part of the 20th century. Gilbert was in his 70s when he did this work & completed work at other battlefields as well.
My SOURCE for all things weapons at Gettysburg provided me additional information about this weapon which did not appear on the muzzle. I used red to designate that data. The rest is as it appears exactly on the muzzle, starting at the top or 11 o'clock position and moving clockwise.
No. 731 ......PICo ......1864 ......S.C.L. ......816 ......FDY #789 ......GRVS 7RH
No. 731 refers to the Army registration number, a way for the military to keep track of the guns. PICo refers to the Phoenix Iron Company in Phoenixville, PA, the foundry where the fun was manufactured. I believe when the Rebels were able to capture one of these guns, they copied it and produced their own, although this one was federally made. 1864 refers to the date of manufacture even though this is an 1861 model. 816 lbs refers to the weight of the firing tube. This number is on the bottom of the muzzle. Each gun is usually very unique and has its own weight which distinguishes it from every other gun, like a fingerprint. Many of these rifles are of the same weight (816 lbs) so the foundry must of had some advanced technology to manufacture rifles with such uniformity. S.C.L. are the initials of the inspector who gave the gun a once over before it was shipped out to the Federal army. The initials stand for the very famous Union Army Inspector Lieut. Colonel Stephen Carr Lyford. FDY #789 is information not found on the muzzle but provided by the website. This is an internal control number specific to the foundry. The carriages were approximately 900 pounds which makes this entire weapon over 1,700 pounds. The GRVS 7RH, more information provided by my source, refers to number of rifling grooves, left or right twist. In this case, 7 right hand twists were made to rifle this cannon. If you were to look closely at the close-ups of the muzzle stamps, the rifling grooves are easy to discern.
About the Foundry
The Phoenix Iron Works (1855: Phoenix Iron Company; 1949: Phoenix Iron & Steel Company; 1955: Phoenix Steel Corporation), located in Phoenixville, Pennsylvania, was a significant manufacturer of iron and related products during the 19th century and early 20th century. Phoenix Iron Company was a major producer of cannons for the Union Army during the American Civil War. The company also produced the Phoenix column, a significant advance in construction material. Phoenix Iron Works is a core component of the Phoenixville Historic District, a National Register of Historic Places site and in 2006 was recognized as a Historic Landmark by ASM International. SOURCE & SOURCE
About the Inspector
Born on August 15, 1838 in New Hampshire, Lyford graduted from West Point on June 24, 1861 and served with distinction as a Lieutenant Colonel throughout the Civil War. He died on May 9, 1885 while on active duty in command of the Rockford Arsenal, Pennsylvania. He is buried in Section 1, Site 9 at Arlington National Cemetery.
SOURCE I also found this biography: Stephen Carr Lyford (New Hampshire) was commander of the Cairo, Illinois, ordnance depot from February to May, 1862, and chief of ordnance in the Department of Tennessee from July 11, 1862, to September 6, 1863. Lyford returned to West Point as assistant professor of mathematics (1865-1867) and as instructor of ordnance and gunnery (1872). In 1874, he went to Japan, where he presented the emperor with arms and books. At the 1876 International Exhibition in Philadelphia, Lyford was a judge for sporting arms, weapons, and explosives. He died at the Frankford, Pennsylvania, arsenal, which he commanded, in 1885. SOURCE
About the Gun
The second most common rifled field artillery in both Armies generally, and the most common on the Maryland Campaign, the 3 inch Ordnance gun was made of hammer-welded, formed, machined iron. It was popular because of its accuracy and reliability, at least those examples built in Federal shops. Less precise machining and lower-grade iron gave their Confederate counterparts more trouble. Those built by the firm of Burton and Archer were know to be problematic. The 3-inch rifle normally fired Hotchkiss or Schenkel shells that weighed between 8 and 9 pounds. In an emergency it could use 10-pounder Parrot ammunition. It could also be used to fire cannister but, as a rifle, was not as effective with this as howitzers or Napoleons. The maximum range of this weapon was 1830 yards, with the barrel/tube Length 69 inches, the bore 3 inches (hence the name) and the total combined weight (already mentioned above), approximately 1720 pounds. Johnson, Curt & Anderson, Richard C., Artillery Hell: Employment of Artillery at Antietam, College Station, TX: Texas A&M University Press, 1995; and
Schwartz, Peter, Artillery at Gettysburg online. SOURCE & SOURCE.
The inscription on the monument which details the regiments action during the war and here @ Gettysburg reads as follows:
(Front):4th Ohio
Infantry.
1st Brigade,
3rd Division,
2nd Corps.
Carroll's Brigade.
Ohio's Tribute.
(Left):On the evening
of
July 2, 1863.
Carroll's Brigade
was sent from its
position with the 2nd
Corps to re-enforce
this position of the
line, and this monument
marks the position
where, as part of that
brigade, the 4th Ohio
Infantry at that time
participated in repelling
an attack of the enemy.
Carroll's Brigade.
Companies A & B, from Mt. Vernon,
Knox County.
Companies C & I, from Delaware,
Delaware County.
Companies D & G, from Kenton,
Hardin County.
(Right):Gettysburg
July 2 and 3, 1863.
Killed.
Capt. Samuel J. Shoub, C I
Lieut. Addison H. Edgar, Co. G
Corp. John Debolt, Co. B
Private James W. Harl, Co. A
Private William Bain, Co. G
Private George H. Martin, Co. G
Private Asa O. Davis, Co. G
Private David W. Collins, Co. G
Private Andrew Myers, Co. G
Private Simon Rollenson, Co. I
Private Jacob Sheak, Co. I
Private Henry C. Stark, Co. I
Wounded.
Capt. Peter Grubb, Co. G
Sergt. M.V.B. Longworth, Co. G
Corp. Lyman S. Ensign, Co. F
Private Wm. D. Breyfogle, Co. C
Private Samuel Wells, Co. C
Private Finley Bain, Co. C
Private James Holloway, Co. D
Private Reason Gillmore, Co. G
Private Michael Hermann, Co. G
Private Henry P. Pfeiffer, Co. G
Private Wm. Shinderwolf, Co. G
Private George W. Wilcox, Co. G
Private John Winstead, Co. I
Private Jacob Boyer, Co. K
Private Joseph Short, Co. K
Carroll's Brigade.
Companies H & K, from Marion,
Marion County.
Company E, from Wooster,
Wayne County.
Company F, from Canton,
Stark County.
(Back):Principal
Engagements.
Rich Mountain
Romney
Blue's Gap
Winchester
Front Royal
Harrison's Landing
Fredericksburg
Chancellorsville
Gettysburg
Bristoe Station
Robertson's Tavern
Mine Run
Morton's Ford
Wilderness
Laurel Hill
Spottsylvania
Ny River
North Anna River
Totopotomoy
Cold Harbor
Carroll's Brigade.
Organized for three months' service
at Columbus, Ohio, April 21, 1861.
Reorganized for three years' service
at Camp Dennison, Ohio, June 5, 1861.
Mustered out at expiration of term
This area is crazy-stupid w' all types of cannons, guns and monuments as far as the eyes (or binoculars) can view, a veritable outside museum. Allow up to an hour or more to fully inspect all there is to see.
