This is a 3rd Model Colt 1851 Navy with the small trigger guard. Serial number is in the 50,000 range and was made in 1856. Standard 1 line New York Barrel Address. Its also an early US Government Purchase as the left side of the frame bears a partial "US" stamp. Various parts show sub-inspector initials "H"...including 2 places on the grips. All matching numbers throughout including barrel wedge, arbor pin, and even the grips! Usually, grip numbers are unreadable due to oil and dirt obscuring the fragile ink numbers. This one survived because someone was smart enough to preserve them by applying a little bit of varnish over the numbers.
Overall condition is NRA Antique Good but not collector grade. If this old pistol were a classic car, it would be well-optioned, daily driver in perfect running condition. On the plus side, its a real US 51' Navy that's all original with Very Good+ grips with good wood to metal fit, nice bore with strong rifling, and great mechanics. Best of all, its a good looking Navy revolver....edges aren't terrible or rounded over, metal is mostly smooth, screws are all good, and its tight...no barrel wiggle or play. However, the metal has been cleaned and then aged to a soft grey patina that's beginning to turn dark. No cylinder scene remaining with some light pitting. Safety pins are mashed (which is common). Brass guard and backstrap are in decent shape but no silver plate is remaining (except internally). Markings are mostly legible with exception of the "U" in "US" on side of frame. Grips have nice sub-inspector marks but no signs of a cartouche (I don't think it ever had one).
This would make a great addition for a collector on a budget who needs a Martially marked 1851, a re-enactor, or something to display without the worries that go along with those expensive high-end example.