These cannons are much smaller than the other Confederate cannons used here in 1863. The tubes are black, very smooth, in terrific shape and represented at the time, some pretty serious weapon technology. The carriages are also equally pristine. This is an 1861 model but was manufactured in 1863. This model was also mass-produced by the Confederates, once they got their hand on a Federal version. I found it to be rather interesting that this gun is supposed to represent the Confederate weaponry deployed at this position, yet it is a Federal gun, inspected by a Federal officer. So much for authenticity at Gettysburg. In fairness, it must be difficult to locate these guns in the 21st century so I am sure they are doing the best they can. The stamp on this muzzle was worn at the 12 o'clock position and it took some investigating and process of elimination to narrow down and eventual figure out the identity of this weapon.
Calvin Gilbert owned a Foundry which bore his name in Gettysburg. This man was responsible for creating all of the cast iron battery tablets (including this one) at this park. 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, 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 and competed work at other battlefields as well.
The two 3-inch guns and the Jordan's Bedford Artillery monument are southwest of Gettysburg and located on West Confederate Avenue, on the left or east side if traveling south southwest, 150 feet north of the Confederate Avenue Observation Tower; the monument faces a westerly direction. The two 3-inch cannons flank either side of the tablet. They were recently removed for maintenance so they are in terrific shape. These guns are supposed to represent the armaments used by this battery during the Battle of Gettysburg. The gun registry information is stamped on their respective muzzles. The left cannon is No. 603 and the right cannon, No. 510. 
Parking is available at the side of the road at small, intermittently placed cutouts. Please do not park on the grass, park on the side of the road. I cannot emphasize that enough! You will be ticketed. The observation tower also has parking for fifteen cars in a dedicated parking area. I visited this monument on Saturday, March 10, 2012 at 3:51 PM, just before the clocks were set ahead for the Spring. I was at an elevation of 607 feet, ASL.
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, 12 o'clock position and moving clockwise.
No 510 - PICo - 1863 - T.T.S.L. - 816 - FDY #544 - GRVS 7RH
No 510 refers to the Army registration number, a way for the military to keep track of the guns when it took receipt of each weapon. 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. (More on that below) 1863 refers to the production date. T.T.S.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, Major Theodore Thadeaus Sobibski Laidley. 816 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. For some reason, there are a whole bunch of these guns with the same weight. I am unsure how that is even possible given the lack of precise manufacturing technology foundry's had in 1863. The weight of this gun is significantly lighter (about 300 pounds) than some of the Confederate Napoleons used during the Battle of Gettysburg. FDY #544 is an internal control number specific to the foundry. The carriages were approximately 900 pounds which makes this entire weapon approximately 1,700 pounds or so. 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.
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
Theodore Thaddeus Sobieski Laidley (1822 - 1886) was an army officer specializing in ordnance. He was also an inventor and author. Laidley was born in Guyandotte, Virginia April 14, 1822. He graduated in 1842 from the U.S. Military Academy and chose a commission in the ordnance corps and served in the Mexican War. At the end of the war, he returned to the arsenal at Watervliet, New York, as Assistant Ordnance officer. Laidley was put on detached service to write a new ordnance manual published in 1862 which served as an important guide during the Civil War. He served on several ordnance boards designing and testing weapons, taking out eight patents. He was later president of the commission to test the strength and value of all kinds of iron, steel, and other metals at the Watertown, Mass. arsenal 1871-1881, retiring in 1882. Laidley wrote government reports and A Course of Instruction in Rifle Firing, Philadelphia, 1879. Theodore Laidley died in Palotka, Florida April 4, 1886. He was inducted into the Ordnance Hall of Fame in 2008. SOURCE, SOURCE, & 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 tablet, which marks the position of Jordan's Bedford CS Artillery Battery on July 2-4, 1863 and narrates those events reads as follows:
Army of Northern Virginia
Longstreet's Corps Artillery Reserve
Alexander's Battalion Jordon's Battery
The Bedford Virginia Artilery
Four 3 inch Rifles
July 2 Took position here 4:30 p.m. Fired a few rounds at the Peach Orchard. Joined the infantry charge and afterwards occupied position on crest near the Peach Orchard and was actively engaged until night.
July 3 Remained near the same position which was on the main artillery line took part in the cannonade preceding Longstreet's final assault and aided in supporting that assault. Retired from the front after night.
July 4 In position near here until 4 p.m. Then withdrew to Marsh Creek on Fairfield Road.
Losses serious but not reported in detail.
This area is loaded with all types of cannons and guns, a veritable outside museum. I would suggest allowing up to an hour to fully inspect all the tablets, monuments and weapons in this area.