Pulling a carbide button thru the bore is a form of burnishing. We do it every day on hydraulic cylinders. Much cheaper than grinding and it also imparts a slight hardness and wear resistance to the surface. Your not pushing metal anywhere, just filling the scratches the reamer left.
Quoted from a machinists web site:
"Burnishing is a process by which a smooth hard tool (using sufficient pressure) is rubbed on the metal surface. This process flattens the high spots by causing plastic flow of the metal. Burnishing improves the surface finish, surface hardness, wear-resistance, fatigue and corrosion resistance. "
The effect on the part is entirely dependent on the material used, what its to be used for and how much undersize the hole is compared the the button.
I might add that gun barrels are not hydraulic cylinders and the purpose they are put to is radically different. Residual stress in a hydraulic cylinder is not going to effect how accurately it shoots. While burnishing will not impart the stress that a full blow button rifling job will its not the best way to smooth a barrel since it will impart stress to the part..
Buttoning a gun barrel does not remove reamer scratches or even fill them in completely.
I have lapped a big name button rifled barrel that was so screwed up on the inside that pulling a lap through the barrel would cause it to "ring" as it ran over the "ironed down" reamer marks.
The ONLY reason to button rifle a rifle barrel or burnish with a button is COST and SPEED of production, quality is a secondary consideration. Button rifling a barrel takes SECONDS. Yes button rifled barrels can be very accurate. But they will not consistently shoot as well barrel to barrel as a cut rifled barrel will and they are more prone to leading when shooting cast bullets even though the barrel has been "ironed" smooth by the button. There are other issues involved such as pushing or pulling the button, driving it with gears or letting it drive itself to set the twist. Then there are factors like torque on the rod as its pushed or pulled or twisted.
Drilling and reaming are the time consuming part. This can be bypassed by hammer forging barrels from a donut of steel. Still will not produce as consistent a barrel as cut rifling. But its cheaper since no deep hole drill or reaming is needed and when people see "forged" they mistakenly think it means higher quality. Its just a cheap way to may a run of the mill rifle barrel. Of course there are stresses imparted here as well and these need to be eliminated in a rifle barrel.
Dan
