Fluted Barrels

[SCW22]

Hope this is the correct section.

I had a custom barrel fitted to my sako however there has been a problem with it coppering up badly after a few shots, we are now trying different bullets to see if this will cure the problem.

The barrel was supposed to come from Walther already fluted however it was not and was fluted in uk and not by walther. Having spoken to a couple of very reputable smiths they have said that the fluting should be done first by the manufacturer and of done after can cause problems due to excess stress when being fluted on the rifling.

Just wondered if anyone else has come across this?

Cheers. steve

 

[Millsaps75]

Metals have internal stress. When you remove material dimensions change.The amount of change depends on the amount of stress.I've been told when you flute a barrel after the bore is finish machined that it will open up. I cut some really deep flutes on a friends 308 hv barrel. He said it actually shot better afterwards. I doubt it had anything to do with the flutes thought.

 

[Larryh128]

Don't doubt that it could shoot better, you very well could have relieved some stress that was affecting accuracy. Can fluting change stresses? Yes, but there is no way that it is changing the internal dimensions or the texture of the barrel. I would be very suspect of whose barrel that you actually have.

 

[LHSmith]

Fluting and turning down the barrel OD CAN change bore dimensions which is why barrel makers prefer to finish the contour and/or flute before lapping. However, cut-rifle barrels are the least affected by changing outside dimensions.

 

[Larryh128]

Microns?

 

[LHSmith]

Microns?

Hart, Lilja, and Krieger all state "when contouring a blank, the interior dimension will increase". Hart and Lilja recommend that they flute a new barrel (if so desired), so that it can be done before the final lapping so as to maintain the finish barrel meets their guaranteed specs.
How much will fluting change the dimensions? Well, Lilja's guarantee is "uniform dimensionally to 0.0001".
Apparently the change in bore dimensions is closer to ten thousandth's of an inch.
Shilen will NOT flute a bbl., nor recommend it , stating "Fluting a bbl. can induce unrecoverable stresses that will encourage warping when heated and can also swell the bore dimensions, causing loose spots in the bore."
Many times you can actually feel these loose spots with a tight fitting patch.
The idea that a drilled hole COULD actually get bigger if the parts OD is reduced (given a constant temperature) is a concept that is hard to grasp.....but my Smith, who works for a Military Parts supplier, and works in tolerances in the 0.0001 region confirms that it is indeed a fact.

 

[Larryh128]

I would certainly like to see someone actually measure it. IF that was a problem blanks would be contoured & then drilled & reamed, not the other way around. I personally don't believe that the main barrel maufacturers can measure the interior of a barrel that close. At .0001 you are in microns.

 

[LHSmith]

In the Sept. "06 issue of Precision Shooting, James Mock authored an article on an interview with John Krieger of Krieger Barrels. In the article it was mentioned that both mechanical and air gauges are used, the air gauge being sensitive to 0.000025 inch, and that the mechanical gauge will tell you things that an air gauge cannot.
Also of note in the article. Krieger is different than most in that they contour the bbl. before drilling it, finding it easier to keep the drill centered and straight. After deep drilling the hole is reamed, then pre-lapped to remove tool marks, then the rifling cut ~0.0001" per pass. A second lapping operation brings the lands and grooves to proper size.