These rifles 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 and the right trunnion reads, Phoenix Iron Co.. The trunnions are sometimes devoid of markings, like this rifle. 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 rifle was manufactured in 1862 so I suppose the rifle saw action during the Civil War and quite possibly here 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. This rifle is interesting as there appears to be a cannon ball stuck in the muzzle.
The 1st New York Independent Battery Monument & rifles are located along 
Hancock Avenue (RD310), on the left or west side of the road if traveling traveling north. The monument is 59 feet to the south of the High Water Mark Monument (MN230). The monument is flanked by two 3-inch ordnance rifles. If facing the street, to the left of the monument is rifle no. 107 and to the right, rifle no. 205. Both rifles point to the west in the direction of the once advancing enemy during Pickett's Charge. This area is an absolute beehive of activity as this site represents the best of what Gettysburg has to offer, both historically and monumentally. 
Parking is plentiful and is available road-side at intermittently enlarged shoulder cut-outs, usually marked with white striping. Be sure to keep vehicles off the grass or you will be ticketed by park police. I visited the rifles on Tuesday, August 7, 2012 at approximately 4:56 P.M. I was at an elevation of 614 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 and 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 the 11 o'clock position and moving clockwise.
No. 205 ......PICo ......1862 ......J.M.W. ......817 ......FDY #216 ......GRVS 7RH
No. 205 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. 1862 refers to the date of manufacture even though this is an 1861 model. 817 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. For some reason, this firing tube is a pound greater.J.M.W. are the initials of James Madison Whittemore, the inspector at the Phoenix Iron Company who gave the gun a once over before it was shipped out to the Federal army. FDY #216 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
James Madison Whittemore was born March 5, 1836. Whittemore was a cadet at the Military Academy from July 1, 1855, to July 1, 1860, when he was graduated and was promoted in the Army to Bvt. Second Lieut. of Artillery, July 1, 1860. He then served in garrison at Ft. Monroe, Va., 1860-61. He was transferred to the Ordnance Corps, May 5, 1861. He served his entire life in the military, eventually commanding the Frankford Arsenal, retiring by Operation of Law, March 5, 1900. (Brigadier-General on Retired List, April 23, 1904) He lived in New Haven, Connecticut upon his retirement. He died, Sept. 6, 1916, at Jamestown, Rhode Island at the age of 80. SOURCE
A portrait and a comprehensive obituary of Whittemore can be found in in the Annual Report, Association of Graduates, for 1917. The United States Military Academy has a complete digital archive of their records and every yearly publication and among those records was that annual report, which can be found HERE. Whittemore's portrait is on page 60 and his obituary is on pages 61-62.
James Madison Whittemore was born March 5, 1836, in Brighton, Massachusetts. His ancestors were prominent in colonial and revolutionary times. His father was a doctor and he had completed his first year in the Lawrence Scientific School of Harvard when he received his appointment to West Point. He entered the academy in 1855, graduating in 1860, the course at that time taking five years.
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.
About the Battery
The 1st New York Independent Battery served as a member of Tompkin’s Brigade in the Sixth Corps, Army of the Potomac. The battery was commanded by Captain Andrew Cowan (1841-1919). Cowan was born in Scotland and was a student at Madison University in New York City. He as wounded during the Petersburg Campaign. Andrew Cowan left the volunteer services as a brevet lieutenant colonel, this promotion dated April 9, 1865. After the war he was a locally prominent businessman. He was also heavily into politics and was involved with various monumentation and their dedications at Gettysburg. He met with at least two presidents. Andrew Cowan died in Louisville on August 23, 1919 at the age of 78.
Under Cowan's command, there were 113 men engaged at Gettysburg with 6 ordnance rifle and among the men, 4 were killed and 8 were wounded. In reserve at first, on July 3, 1863 it was placed just south of the copse of trees on Cemetery Ridge, in time to resist Pickett's Charge. Cowan’s guns filled a gap in the infantry line left when a regiment left the front. Cowan ordered his men to fire double canister on a group of Confederates trying to penetrate the federal line, and their fire broke up that threat. Eventually the unit was honorably discharged and mustered out June 23, 1865, at Syracuse, having lost by death, killed in action, 1 officer, 12 enlisted men; of wounds received in action, 1 officer, 6 enlisted men; of disease and other causes, 38 enlisted men; total, 2 officers, 56 enlisted men; aggregate, 58; of whom 1 enlisted man died in the hands of the enemy.