From 1850 through 1856, many of the contract muskets in store at U.S. arsenals were altered from flintlock to percussion by means of "Belgian" or "cone-in barrel" method. System of alteration involved removal of flintlock battery from the lock, filling in the screw holes from those parts, substituting a percussion hammer for the cock, plugging the vent, removing the breech plug so as to "upset" the upper right-hand side top of barrel, drilling and threading the "upset" section for a cone, reinserting breech plug and screwing in a new percussion cone. The percussion musket was effective, but the barrel was considerably weakened by this process. While some were rifled during the American Civil War, most saw service in that conflict as smoothbores. As a general rule, muskets so altered generally command about one-third the price of the arm in original flintlock. Exceptions are those with state ownership marks (e.g., "OHIO" in the stock), with regimental marks, or with so-called "Sea Fencible" buttplate.