This is a very early, pre-patent Model 1839 Colt Paterson Rifle with a 32 inch barrel ,.52 caliber smooth bore, and a square back cylinder.  This gun would have been produced in 1838 prior to the issuance of the Model 1839 Revolving Long Arm Patent.  The long barrel and the square back cylinder are extremely rare and if you will notice in the final photograph, there is no retaining ring on the cylinder pin to hold the ratchet in place.  I have never seen a Model 1839 without that feature.  Normally the  retaining ring, which the ratchet bears against is affixed to the cylinder pin by a screw which fits in a hole, drilled all the way through the pin.  On this gun, there is no retaining ring nor is there a hole drilled through the cylinder pin to affix it by.  The ratchet is extended further forward than normal, the cylinder pin has a groove machined in it and there are three set screws which screw into the ratchet collar that ride in that groove, thus holding the ratchet in place.  The rear of  the cylinder has a machined recess, which fits this assembly.  I have never seen this configuration and can only surmise that this gun was built before the final configuration, which is in the Model 1839 patent drawings, was worked out.  You might say it is sort of a prototype, a developmental variation.  The basic gun is serial number 76.  This number can be found on the lower and upper frame, the ring plate, ratchet, hammer, upper tang, back of the cylinder and is partially visible on the back of the barrel.  The wedge is serial number 73 and the butt plate is serial number 82.  The fact that these numbers are all so close together tells me that this gun was probably assembled in this configuration at the factory, to work out the final design.  It is in a nice brown patina with considerable traces of the original barrel address showing on the right side of the barrel lug and has very good mechanical function.  There may be some very minor chipping repair on the stock along the upper tang.  The gun is an honest, historic and extremely rare example of a Model 1839 Colt Paterson Revolving Arm.  SOLD!!