They were made using the melted down blue-grey steel of the sword, Excalibur, and have the rose, the sign of the Eld, engraved in the side. The sandalwood grips of the gun have never lost their fragrance and near the muzzle of each gun can be seen scroll work which translates to "White", which was Arthur's dihn mark.
However there are many other legends to their exact origins and some say the steel and sandalwood are not from Mid-World and brought from an alien world. Other believe the guns came from same Kashamin pyramid that Arthur and his sword Excalibur has been entombed in, with others saying they were a gift from the Dark Tower.
The guns are extraordinarily large by the standards of modern pistols. They are described multiple times as being "comically large". The guns shoot .45 caliber bullets and our world's equivalent of Roland's original bullets are Winchester .45's.
A few times in the series, Roland has referred to the guns as "the widow makers".
From the way they are usually depicted and described, they are likely twins of the Colt Single action army model, otherwise known as The Peacemaker or the SAA in .45 Long Colt. They are described in operating in ways that typical cowboy style guns can not. That is, the cylinder does not swing open and the hammer must be cocked by thumb before firing. Modern revolvers called double action can be fired and reloaded this way, but it is pretty clear King means to use the Colt SAA as Rolands Guns.But in Midworld, anything is possible.