Generally, the longest lasting and most durable, cold hammer-forged barrels are constructed by impacting a barrel blank thousands of times with industrial hammers at room temperature to lengthen it into the proper shape for a firearm. This method is also used to install the rifling inside the bore, with the hammers forming the barrel around a mandrel that cuts the internal rifling grooves. The constant pounding from the forging process helps unify the molecular structure of the barrel material making it less susceptible to wear under high use and does not require the break-in period that other barrel manufacturing methods require. Many high-end rifles come with a cold-hammer-forged barrel as do some handguns. However, most rifle barrels are constructed from a cylinder of steel, machined to the proper contours. The grooves inside the bore are inserted typically using either the button rifling method or broach rifling.