More questions on contouring

[flintlocke]

The contour/chatter post, excellent responses and I'd like to ask further questions. Over the years, I've had a couple guys request that I turn the steps off Mauser barrels, which I did, following best practices with light cuts and modest tailstock pressure and a well adjusted steady rest. I don't think I bent any barrels from poor practices, yet both guys kind of gave me the stinkeye when they shot the new profile and told me they had lost some accuracy. One of the guys is a master reloader and well understands that he would need to deal with a different barrel harmonic after turning and both guys adjusted bedding.
So, my long winded question, is this something that happens frequently when re-profiling? In both cases they were Mauser original barrels, and I don't know if these originals were heavily stressed in manufacture, or if I did something wrong or 'tis the nature of the beast. Thank you for sharing your experiences, Paul

[M-Tecs]

Generally that's the nature of the beast. That is more true of mass produced barrels than something like a Krieger that is double stress relieved. There is a reason that they recommend fluting an or profiling before rifling.

Normally when you remove material from the OD the ID will increase inside due to stress relief. Barrel walking can become an issue also. On the other hand sometimes you have zero noticeable effects.

[Winger Ed.]

Interesting.

Over the years, I've become less inclined to change something and try to re-invent the wheel.
If I was going to rebarrel one of those, I'd get a aftermarket barrel from a source that had a good reputation for making them.

For the originals, and how successful their design is:
I'd presume they had it figured out, and 'all the King's men' & 'all the King's horses'
really did know what they were doing when they arrived at the design,
and then made a few million of them that have all stood up well to the test of time.

And me hacking and chopping around in the garage changing it probably wasn't going to come out well.

[country gent]

Several things change when contouring a barrel. a change in contour can and will change the stress patterns in the barrel affecting harmonics but also sizes in the bore. Localized changes may result in tight or loose spots. Another is if the bore isnt straight thru the barrels center then the wall thickness will vary turning smaller will make this more obvious. Lighter barrels are more likely to walk shots as they warm. Turning a contour may also create some work hardening in the blanks.

Those old military barrels had a lot of stress in them from the manufacturing process, equipment of the time, and steels available. They were made fast and to specs more open than sporting rifles or target grade firearms. All of this has an effect on your results when re-contouring a barrel.

[flintlocke]

Well thanks fellas, everything you say, when I stop to think about it is absolutely true, intuitively. But, when a man from Gun Barrel City Texas chimes in....only the most imprudent fool would not heed his advice. Grin.
As I think about this further, to shave off an ounce in the name of cosmetic appeal with a good chance of degrading the accuracy, it just doesn't make sense. My wife has a pair of cowboy boots that just kill her, yet she wears them because they look nice....just wrong.

[Jedman]

I work a lot with major brand take off barrels and out of DOZENS of them I have yet to see even 1 where the bore is within .005 concentric to the OD. Many are .020 + when indicating the OD while the chamber and muzzle are between centers.
I turn these into thick wall barrel liners and usually flip these end for end 3 - 4 times while turning the OD and each time re-indicate and reseting the steady rest.

Jedman

[Willbird]

Those old military barrels had a lot of stress in them from the manufacturing process, equipment of the time, and steels available. They were made fast and to specs more open than sporting rifles or target grade firearms. All of this has an effect on your results when re-contouring a barrel.

Also comes to mind that it was very common practice to straighten barrels back in the day during the mfg process. or more like "bend them straighter after all the work is done" :-).

Bill

[country gent]

In one of Elmer Kieth books he told of gauges used to select the star gauge barrels for target and sniper rifles, He then went on to describe the straightening press used on the other barrels. This was set up near an outside wall with a row of windows the inside frame formed a cross and the workers would look thru the barrels at the cross to see if was round hole or oval and each gad an old screw thread press straightener. They would look thru barrel and find the high spot then in the press and move it what they thought it needed then look again this was repeated till they seen a round hole. The Star gauge were selected on straightness and tight dimensions. I have seen barrels a pin gauge would enter muzzle and breech and a short pin the same dia 3/4-1" long would slide down the bore but a 4" long pin gauge stopped in vot passing thru.This indicates a bore thats not straight. when the short pin passes but a longer the same size dosnt.

Old machinist would hang weights on long parts to relieve chattering also, Its amazing what effect a couple pounds on a shaft has just hanging their from a bushing or bearing, Another help relieving chatter is a spring loaded center, When the center is "set" on a long cold shaft it is at the shortest point. as its turned it warms and expands getting longer this expansion in length can be .005-.010 on longer piece since the solid center is locked it forces the part to bow or bend causing chatter. he spring loaded center allows the part to expand and maintain tension with out increasing the tension.

[samari46]

There was an article in the old Precision Shooting magazine about the steps on the mauser barrels. If I remember right they were there for a purpose. Something to do with vibration nodes. And if you turned them off the barrel may or may not shoot as well after they had been turned off. Frank