After the barrels are rifled they are stress relieved in a vacuum furnace. When a barrel is button rifled, no material is removed to create the grooves. Rather, the steel is cold formed and moved outward. This process introduces some stress into the steel and the stress then must be removed. The best method of doing so is by heating the barrel to a temperature of about 1100º F. and holding the steel at that temperature for a predetermined time. To prevent decarburization of the steel it is best to perform this step in a vacuum furnace where the atmosphere is pumped out. Following this heat treating operation the barrels are completely stress free. One of the specifications Lilja gives the steel mill is a stress relieving operation, performed as their last step in producing the steel. So, all Lilja barrels have been double stress relieved, once at the steel mill and again after rifling.