Under what situation(s) is turning down a factory barrel more desirable than having a new barrel turned to the desired contour? The reason that I ask is that I was reading through some descriptions of some of Jack O'Connor's "favored" rifles and I noticed that for about half of the M70's listed he had them rebarrelled and half the time the factory barrel was turned. Why one method vs. the other? In his case (as it would be for me) I would tend to doubt that the rebarrelling was out of a desire for a heavier contour. Any thoughts?

Thanks,
Bob

TYurning down barrels was done a lot when people were "sporterizing" a lot of military weapons. Mausers and Springfields were altered this way a lot. Such turning often released stresses unevenly, causing barrels to warp, or worse, making them "walk their groups" when they heated up during firing. It was discovered that such problems could sometimes be avoided by turning them down slowly, tking off just a little metal on each cut.

For some reason reboring a barrel to a larger diameter often results in a more accurate barrel, while cutting material from the outside of a barrel just as often has the opposite effect!

Been considering lightening up a Varmint barrel in 7-08. My daughter may carry it soon. I know for fact it is clumsy to carry with a light stock.. Muzzle heavy,,,, Though I do not want to screw up the accuracy,,, Prints little tiny holes..
Looks like I am going to re-barrel, not turn...

You need to look really think the consequences all the way through before acting...

As previously stated, turning down a barrel can induce problems.It takes a highly skilled person with a lathe and good knowledge of metals to do the job correctly. The central problm is that as metal is removed, the friction produces heat which causes the barrel to grow a might and unless the tailstock is backed off to compensate for this extra length, a bow will develope with the result that the new outside contour is not concentric with the hole in the middle. How was that for a run on sentence! There are some barrel makers whose warantee will be voided if the barrel is turned down after it leaves their shop. That ought to tell you something.

Some barrels are crooked before you turn them. Like my 264 WM. I wanted to turn it to lighten it but a careful look down the bore reveals a slight curve in it. It shoots acceptably now. It starts walking up after 3 shots, but it is a hunting rifle so it isn't really a problem. Turning it down would probably ruin it completely.

I agree with eldeguello, but I'd add one thing.

I have been told (by a barrelmaker who makes both button rifled and cut-rifled barrels) that a cut rifled barrel may be (slowly-- to avoid overheating) turned down and will not affect accuracy. On the other hand, a button-rifled or hammer-forged barrel has a lot of internal stresses that will make themselves known if the outside is turned down. He does NOT recommend turning his button-rifled barrels very much at all!

He thinks that cryogenic treatment MAY allow the latter two types of barrels to be turned down by removing these stresses, but he is sceptical of the procedure...

For what it is worth,

jpb

Maybe a dumb question, but... If turning a barrel induces all these stresses, how do they turn the first/factory contour without putting these stresses into the barrel? Why would returning the barrel be any worse than turning it the first time?

Bob

I've had four or five barrels turned down and they all shoot very well. The machinist (my little brother) has twenty five years of experience and knows what he's doing.

Probably half the barrels I put on are either turned out of the blank or a recontouring of the factory contour. Any decent barrel of modern manufacture can be turned down with little difficulty. The only time problems may arise is when the barrel was not properly stress relieved as part of the manufacturing process. I have contoured barrels which were buttoned, broached, cutrifled, and hammer forged and all have been just fine. I once had a few barrels from one manufacturer which were obviously not stress relieved and it was a real battle to try and contour those. Often they would suddenly develope a .050 bow halfway through the cut.I finally put them in the cooking oven and turned it up as high as it would go and cooked them for a few hours. While this was not enough temperature to do a thorough stress relieving job on them it was sufficient to make the job possible.
The only real difficulty is in getting the tool to cut well enough that the barrel doesn't chatter.
Some have said that when they turned Remington barrels down they found the bore to be crooked. I figure chances are it was crooked to start with!
Often a barrel which has been recontoured will shoot just as well as before but not with the same load. This is simply due to a change in vibration frequency. Regards, Bill.

Mauserkid,
What r u going to do with the barrel you remove? Small Holes???

Barrel turning in the "olden times" to change factory contour, get rid of ripples or whatever reason. The comment about the barrel surface being heated and inducing new stresses is mostly a crock. If the cutting tool is designed out of the book for straight turning of a solid bar this could lend credence to that largely old wives tale. The idea is to make the cutting tool in such a way that it puts all the heat of cutting into the chip and not in friction where it rubs on the barrel just past the cutting edge. Biesen and I comiserated with one another usually over a beer or more every time we got stuck with having to turn down a 70 Win barrel made with the integral front ramp. It was quite rare to find one that wasn't wilder than a march hare. Frequently, in 2 inches of turning length it would walk as the INTERNAL stresses were relieved. This meant a trip to a shop with an arbor press and your handy dandy blocks used to keep from squashing the barrel. The problem with these barrels and others of the time was that the barrelblank was a forging because of the forged ramp and the band ahead of the receiver for the sights and forend tie down. These were annealed because of the forging temperature then re heat treated and normalized. What they needed was Iso-thermic step annealing. Too late to do this after the hole was drilled, reamed and rifled. The factory had similar processing problems. Other barrels ( other makes) were usually of a carbon-manganese or roughly 50 carbon "Ordnance" steel. These ( to include Springfields) were not much of a problem. Old cantankerous Bill Sukalle wised up a helluva lot sooner than Al Biesen or myself.
Jack O'Conner always thought that was because Sukalle made barrels. Many times these barrels shot better afterwards because we had cut a few of the tendons in the process and they did not walk during firing. Never trusting anything, I heated them up to where they were about 200 degrees F using a clamped on or a sweated on ramp with sight and a Lyman 48 receiver sight aimed at something 100 yards off, and watched the sights wander as the barrel cooled while locked in 120 pounds of big vise securely mounted to an equally heavy bench. If there was no discernable movement I went to test firing in a stock. The later 70 Win barrels with brazed or soldered on ramps were little different than and sometimes better than today's custom offerings. Bill Leepers comments I can echo.