Cartridges that are commonly improved with +P pressures are the 9mm Parabellum, .38 Special, .45 ACP, .38 Super, and .257 Roberts which are all cartridges that date from the early 20th century. There has been significant improvement in metallurgy and quality since the first guns in those calibers have been made, with the result that higher pressures are now safe in modern firearms. Many models will specify the degree to which they can use +P ammunition; for example, many aluminum alloy framed .38 Special revolvers should not regularly be used with +P ammunition, for while the cylinder is capable of withstanding the pressures, the added force will increase wear and reduce the service life of the gun.