Barrels from aftermarket makers are generally divided into one of two type; cut or buttoned. It refers to how the barrel is made. In a nutshell, a barrel is drilled to approximately bore size, the same in either method. In a buttoned barrel, the lands and grooves are formed by pulling (or pushing, in some cases) a solid carbide "button" through the bore. This button is oversize (as in, won't fit through the bore), and is a mirror reversed image of the rifling. As it's pulled through the bore, it literally swages the rifling into the bore surface, leaving a fully rifled barrel as the button emerges from the far end. One pass, very simple, very quick. In a cut rifled barrel, a single point (generally speaking) cutting head is pulled through the barrel, leaving a very slight scratch in the surface of the bore. Ever heard the term, "starting from scratch"? That's where it comes from; barrel making. Anyway, once the cutter emerges, the barrel is rotated 90 degrees (for a four groove barrel) and the cutter makes another pass, leaving another scratch parallel to the first. This is repeated two more times until there's four identical scratches down the bore. At that point, the cutter head is raised, and it goes down the first scratch for a second time, cutting it deeper. Bear in mind, we're talking millionths of an inch being removed at each pass, not hogging out a full groove in a single pass. The process is repeated in each of the succesive grooves, the cutter reaised again, repeat, etc.. Normally, that cutter will make somewhere between three and four undred passes up and down that bore before the grooves are fully cut. This of course depends on the number of grooves (I used four here, merely as an example), their depth, bore diameter, etc.. You're normally looking at 45 minutes to an hour or so for the production of a single cut rifled barrel once it arrives at the cutting process, where a buttoned barrel takes around ten to 40 seconds, depending on the manufacturer. Cut barrels (at least the better ones) will normally be lapped once completed, where very few buttoned barrels are. Both processes can produce good barrels, but there's advantages and disadvantages to each as well. Take your pick.
The third common method of barrel making is hammer forging, but the machinery and tooling for this is well into the millions, so it's primarily a process for major manufacturers only. Ruger does some hammer forging of their barrels, Winchester did at one time, and I believe Remington is using it for some of theirs as well. Very quick, can turn out a good barrel (I've used dozens of Sauer 202 barrels that were excellent) and they're fairly cheap to produce, once the equipement costs are amortized.
There are, or have been some others, but you don't see them being widely used today. It's an intersting history, and a fascinating process whichever method is used.
