Here is a link to an article about making airgun barrels written by Dennis Quackenbush you might find interesting.
http://www.quackenbushairguns.com/Airgun_barrels.htm
Paraphrased from Dennis Quackenbush's article "Making Airgun Barrels"
" Button rifling is quicker than cutting the rifling, which means it's less expensive to make, but being done quickly doesn't make it of lower quality. The quality is in the detail of how well you want to make the barrel. How much attention do you pay to the process? The quality of the tools and the quality of the material used is what will determine your finished product, not what process you use.
click on picture to enlarge
This picture is a rifling button. To the right side of the picture is the pull rod which extends for another 40" to the right. The pull rod is used because you actually pull this through the bore. You can pull in "tension" whereas you couldn't push a small diameter rod through the barrel in "compression" without the rod bending.
The left side of the picture is the working end of the tool. Tungsten carbide, because of its hardness, wear resistance and non-galling characteristics, is required. The tungsten carbide portion is silver soldered to the tool steel pull rod. You can see the solder line slightly left of center in the picture, just where the grooves begin. The grooved section is what imparts the rifling. It is tapered in the front and the back to a small bearing surface in the middle. This gives a gradual start to the rifling forming, and the small bearing surface keeps the pulling force lower.
The width of the groove is the width of the rifling. The width of the segment between the grooves is the width and bottom of the groove. The button is a negative image of the rifling. The angle of the grooves is what makes the rifling twist rate. A shallow angle for slow twist and a steeper angle for a faster twist rate. Twist rate can be modified, within a small range, by a mechanical set up on the rifling machine that is timed to turn the barrel at a rate that is slightly plus or minus of what the button's rate of twist is. This is how I made a "gain" twist. The barrel blank was turned at the same rate of twist that the button would impress, and as the button approached the muzzle, the blank would be turned slightly faster than the button's rate of twist."
The rifling button may include an “ironing button” or another football shaped “smoothing” button may be drawn through the bore to make/draw the bore diameter to a finished size.
Boomer
