sentences:  Another rarity in the 1851 Navy production is the .40 caliber model, only 5 were made in 1858 for testing by the U.S. Navy Bureau of Ordnance.Sighting consists of a tapered brass cone front sight pressed into the muzzle end of the top barrel flat with a notch in the top of the hammer, as with most Colt percussion revolvers.In spite of the relative crudity of the sighting arrangement, these revolvers and their modern replicas generally are quite accurate.