octagon barrel crown question

J

Jason Shore

Guest
Planning on buying a lilga octagon barrel for a 20 cal build for something different.
I dont see many modern or benchrest guns with octagon barrels.Is there are reason for this or is it just that most people prefer the looks of the round barrel.
I have also seen on a few photos that all the octagon have 90 degree crowns.
Can a 90 degree crown still shoot as accurate as a target crown and what about protection of the 90 degree crown ? As I see it it has no extra protection being at 90 degress.
Any thoughts and imput appreciated
Jason
 
Most BR shooters use a 90 deg. crown. What is a target crown? Cutting an octagon induces stress in the barrel. That ain't good for a competition barrel.
Butch
 
Adding sides to a round barrel is a cosmetic thing. It does not add to accuracy, it requires more work to make it and to index it and to inlet it into a stock... all for the sake of the look... nothing wrong with it if you want it... they do look different.

The flat crown really is not a problem unless you plan on using the muzzle for a walking stick and then a recessed crown won't help much either. I have never understood how the shape of the crown protects it. What are people doing with the muzzle that damages it other than shooting?
 
fitted a whole mess of octo barrels while at Dakota Arms. (Lil sharps rifle)

Use a sharp tool, go from inside to out and have no fear. They'll shoot just fine.


If you try to go with a recessed crown your probably going to find out that the flats on the outside are not concentric/symmetrical to the bore CL. If you indicate off the bore you'll end up with sides that are uneven.

Since it's a 90* crown, where you indicate the barrel has nothing to do with how the crown turns out. If it were a round barrel you wouldn't have to do anything but chuck it up.

Indicate off the flats and they'll all match up nice.

Good luck.
 
Thanks for the replys guys. I was thinking of ordering the barrel directly from lilga with the same profile as the factory remington contour with the only differance the outside shape which will be the octagon shape.
Wont the barrel fit in the stock channel if it is the same diamention :confused:
Isnt a lilga octagon barrel as accurate as one of there benchrest contours :confused:
Thanks Jason
 
I would have to think that any marquee barrel maker is going to ensure that the product is made right before it leaves the shop.

I think you'll be fine.

C
 
If the barrel is made of octagonal stock which is large enough it should be fine. If made of octagonal stock of any size and cut rifled it should be fine. If milled out of a blank, regardless of rifling method, there may be some distortion. I always feel pretty good about turning a barrel down but for whatever reason, milling is different. At least it feels different to me.
Nonetheless, virtually all of the octagonal barrels you see on modern custom rifles are milled from a blank. From a hunting rifle perspective, they work out just fine. Because they are usually milled with the barrel on centers, the bore is usually quite concentric with the outside.
If the flats of the barrel are the same diameter as the Remington barrel, you would have to provide for the corners. If the corners are the same as the Rem contour, you will have gaps on the sides. Regards, Bill
 
I am not a metallurgist, just a practicing metal butcher/machinist. That said, it is my understanding that stress can be introduced to a steel workpiece by cold forming (bending, hobbing, buttoning, extrusion etc.) or by the uneven application of enough heat (welding etc.) to change the heat treatment at different areas of the work piece. The removal of material by machining with sharp tooling using correct cutting speeds and feed rates will not introduce stress to a workpiece which was stress free to begin with and will actually relieve some stress in internally stressed parts resulting in their deformation. This deformation is what buttoned barrel makers prevent by stress relieving (a heat treat process) the cylindrical blanks after buttoning but before contouring. If this step is omitted the bore opens up when the blanks are contoured. Both button and cut rifled barrels start out as stress free bars of steel. The buttoning process introduces internal stress in the barrel which must then be relieved before the blank is contoured. The cut rifling process introduces no stress so the extra heat treat process is not needed. A quality example of either type should work well for your purpose.

The bore can be distorted by improper machining technique also. Cutting flutes too deep or barrel walls too thin when milling the octagonal form can distort the shape of a finished bore. I don't see any real difference between the effects of milling a barrel to octagonal form and cutting flutes in it. With a good rigid setup and sharp tools a quality barrel should be undamaged.

The best way I know to assure yourself of a distortion free bore is to obtain a barrel from one of the shops using the cut rifling method who will machine the blank to your specs (octagonal) externally after it has been drilled but before it is reamed or rifled. Once the contouring is complete, the barrel is reamed, cut rifled & lapped. You should avoid any surprises following this route.

I would love to hear from those more learned in this subject than I. I'm always looking to learn more!

Thanks.
 
dedseven,

What you just said is 100% accurate.

As a manufacturing technology professional, I confirm that no internal stress
is introduced into the metal part after turning, milling, drilling, reaming, broaching, grinding, honning, lapping, polishing, assuming, as you said, that tools are up to specs and metal removal rates are reasonable.

However, if metal blank is machined assymetrically, and blank is not totally stress free, and no metal piece is free of internal stress since birth unless artificial or natural long enough "aging" was applied, such piece will certainly distort. But this is certainly not a direct fault of machining, like you said.
 
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