This revolver was manufactured in 1888, the first year the Flattop Target single Action Army revolver was introduced. Only 925 of these revolvers (in all calibers combined) were manufactured between 1888 and 1896, therefore are highly regarded and sought after by collectors. Even rarer is the fact that only 89 Flattops were chambered in the 450 Boxer caliber. The 7 1/2 inch barrel variation was the most common of this model, so the 5 1/2 inch barrel adds to the rarity of this revolver, as well as having the Hartford and London address marked on top of the barrel. These Flattop Target revolvers predominantly fell into the serial number range of 127,000 to 163,000. Not only rare, these revolvers were a very attractive and well finished variation. The top of the barrel is marked "COLT'S PT. F. A. MFG. Co HARTFORD CT. U.S.A. DEPOT 14 PALL MALL LONDON" with the three line, three patent dates on the lower left side of the frame and "45 CAL/B" on the upper left front of the trigger guard bow. The bottom of the barrel at the breech and around the rear of the cylinder are marked with crown over "V" and "GP" proof marks. Matching serial number on the frame, trigger guard and back strap and the loading gate is marked with the assembly number "18". Removable brass blade front sight and standard dovetailed rear "U" notch target sight. Fitted with checkered Rampant Colt American Eagle relief grips. The accompanying factory letter verifies the Flattop configuration, caliber, 5 1/2 inch barrel, blue finish, rubber grips, and that it was shipped as 1 of 10 to Colt's Patent fire Arms Co. 14 Pall Mall, London, England on December 17, 1888.