Rifle barrel construction explained
A rifle barrel may appear to be just a round piece of steel with a hole drilled through its center from one end to the other. Well, basically, that's what a rifle barrel is.
However, there is a bit more to it than just drilling a straight hole from one end to the other.
Notice that I said a straight hole. When you come to think about it, drilling a straight hole in the dead center of a round piece of steel for up to 36 inches is by no means a simple task. Since I have never done it nor have I seen it done, I can't shed much light on all the complexities. But you can be assured it is not a simple task.
In the very early days before they had drilling machines, barrels were hammer forged around an iron mandrel. Wire was wrapped around a rod of bore diameter, heated red hot and then pounded to weld the hot wire into a solid bar of iron. This worked to some degree, but it was fraught with problems, and the basic problem was staying in one piece when the weapon was fired. Since it took two men to fire the first muskets, both prayed to their favorite saints that the cannon would not blow up.
As the gun became more refined, new methods of installing the hole in the round bar were discovered. It still was no easy job, and getting the drill to run dead center was next to impossible. It still was no easy job, and getting the drill to run dead center was next to impossible. In fact, one barrel maker told me a few years ago that it still a difficult thing to do. He told me if he drilled a barrel perfectly true he called it a Grade A barrel and charged more for it.
With better and more uniform barrels being used on rifles, the next step was to achieve accuracy. At that time, there were no grooves (rifling) in the bore. It was smooth like a shotgun barrel. Some used lead balls slightly larger than the bore and forced them down the barrel. In some cases, actually hammering them down. This deformed the ball, which lost all semblance of accuracy. Another problem that faced the early shooters was powder fouling. Burnt powder adhered to the bore, making it difficult to push another ball down the bore.
Someone came up with the idea of cutting several straight grooves in the bore to collect fouling. I've heard arguments both ways whether this helped or not, but one thing for sure is that cutting grooves in the bore showed promise in the accuracy column. Eventually, the straight grooved method was traded for spiral grooves. It is claimed this was done to make the grooves longer so they would catch more fouling, but that doesn't seem true. It was known that feathers set on an angel on an arrow made it turn. I think some gun builder thought it would do the same for the lead ball.
Putting spiral grooves in the bore was an exasperating procedure.