I'm no expert on guns, but I am a machinist. Do many people machine flutes after the barrel is cut internally??
I would wonder if machining flutes would make the barrel twist slightly. Just because the metal relaxes more when material is removed. Unless that barrel is completely stress free to begin with, and the cutting pressures are very low it may hold its shape. But stress relieving it after, wouldn't that throw off the bore??
I'd like to learn more about this, tell me how they do it.
I don't know jack about machining or gunsmithing but here is an excerpt from Dan Lilja's web page that I found informative.......
Q: Does fluting cause stress in a barrel?
A: We've been asked if machining flutes into a rifle barrel causes stress in the steel. The short answer is no, it does not. There are some operations in the manufacture of a rifle barrel that can cause stress to develop in the steel, but fluting is not one of them. To the contrary, fluting can and will relieve stress if it is already present. The same is true of any outside machining work performed on a barrel.
The type of stress that can exist in a barrel is called compressive stress. Under normal conditions the stress could form from two processes. When steel is manufactured, the round shape is formed through a rolling operation in the steel mill. This forming can be performed either hot or cold. Cold rolling generates a great deal of internal stress in the steel. Usually, with steel used for rifle barrels, this stress is relieved by heating the steel to just below its transformation or critical temperature. We have the steel mill that makes our steel do this as their very last operation, ensuring us that the steel is stress free when we receive it.
Secondly, stress can be formed in a rifle barrel during a cold forming operation, such as button rifling. Since no material is removed from the barrel when the rifling is formed, rather it is displaced, it causes compressive stress in the steel. If this stress is not removed, through a heat treating operation, it will remain in the steel where it can cause other problems. Any subsequent machining operations, such as turning the outside diameter of the barrel, will allow some of those stresses to come out. The result can be an opening of the inside diameter of the barrel, more so towards the muzzle where more material is machined away. It can and probably will also cause the barrel to warp. And if these aren't enough, the temporary heating and cooling of the barrel that occurs during normal firing will also let the stress come out by warping the barrel. Poor accuracy is the result.
Although a barrel would not normally be welded on, this can also cause stresses to form in steel. At times though, gunsmiths will heat barrels to sweat-on barrel bands and sites. Too much heat can cause some problems as well.
But, the fact remains that normal machining operations, such as outside turning, fluting, drilling and tapping site holes, etc. do not cause or introduce stress. They can and do allow residual stresses to come out of the steel though.
We flute about 50 rifle barrels per month and have never had a problem with our barrels related to fluting.
