I agree -- - repro, but old. This type of flask is called a "common top" -- - the shutter is exposed. The "Patent Top" flasks have the shutter operating inside the screw-off top -- - i.e., between TWO brass sheets, therefore less likely to admit a spark when charging the barrel / cylinder.
The majority of British cased Colts came with a "small bag flask" -- oval in cross-section, no embossing to the sides. (See Sutherland & Wilson, page 134) Some of the Dixon-made flasks have the legend "Colt's Navy Flask" engraved on the top of the shutter. Others do not, as Von Offen would not pay the extra for the engraving. The spouts are normally calibrated in DRAMS*** -- e.g., 3/8 4/8 5/8 being for a British 54bore (ca. .44") revolver or for the .36 Colt which took a heavier charge -- the 80bore (ca. 36cal) British revolvers normally had chargers for 2/8 3/8 4/8
VERY occasionally one finds this flask with W (broadarrow) D engraved on the top --- I bought one last week ;-) -- these being for War Department issued arms, most of which went to the Navy for use in the Crimea.
*** Strictly-speaking there are 7000 grains to a pound weight, so an "ounce" was 437.5 grains and 1/16 of that was 27.34 grains.