If I purchase a Shilen stress relieved barrel and then have it machined part octagon part round will that negatively affect the stress relieving?

Any time you cut metal, it will induce or relieve stress. Even if it is stress relieved.

But, the key to it on a barrel, is to do it equally. On a octagon barrel, you want to machine opposite side before doing the next flats.

It shouldn't effect accuracy, done that way. Also the cutting will induce less stress, per cut with a sharp tool so, make sure of that.

If the stress has not been relieved the barrel will warp when you machine on it. All modern barrel makers do a stress relieve on new barrels that I know of. There was one old barrel maker in Kalispell MT. that did not stress relieve his barrels, told me he used stress relieved metal. problem is with button rifled barrels the stress is caused by the rifling.

GunBum wrote on Jul 16^th, 2026 at 8:14am:


I generally cut an octagon barrel like your last comment.  A couple weeks ago I cut the short, 7 1/2 inch, octagon on this barrel for #4 rolling block.  On a short section like this, I cut each flat to within .020 of final size.  I start out taking deep cuts and lighten up as I get a wider flat on the first four.  I cut both ways but do take lighter cuts when climb milling and brake the mill bed.  I use a 1/2 inch 6 flute carbide end mill, side cutting.  This barrel needed, if I remember correctly, .180 off each flat, turning to the off 180 degree side for each operation.  I finish with a couple light cuts on each flat to size.  Finish isn’t as bad as it looks in the picture but I draw file them anyway so really don’t care.  This was a Green Mountain barrel.  Took a couple hours to plow off to the rough size and another hour to finish to size.

Never had a problem doing the machining like this and I don’t use coolant but do use some air to cool.
Bob