This is a small Dixon & Sons bag flask as found with cased Colt revolvers, which are particularly common with London Colts. The cap is marked "James Dixon & Sons Sheffield". Spout is graduated in increments of 4/8, 5/8, and 6/8 drams. Robin Rapley's excellent book on Colt Accoutrements notes that Dixon flasks (F#42) with these graduations are not for the 1849 Pocket but are actually a much scarcer variation used for the 1862 Colt Pocket Navy Revolver. He notes that he's only seen one example with a Colt marking but goes on to say, "This flask with the same charger markings, but without the Colt mark, is correct for Pocket Navy and Police Cases.
Overall condition is Good with the copper body still showing all of its patina. Numerous small dings and dents but overall shape is still nice and the seams are perfect with no splits. Lanyard loop at bottom is missing. Cap and spout are brass and also show a pleasing patina. Spout spring is original and works perfectly. A great opportunity to acquire a very scarce Colt accessory.