Off-Center Bore

sbindy

sbindy

Steve B
I am doing some work to my Savage in .223, and I shortened the barrel to 20". Partly to make the barrel stiffer and shoot better, and to get rid of a spot near the muzzle the fouled badly. After shortening, I noticed the bore wasnt in the center of the barrel anymore, and measured it. One side was .310, the other was .332!

Since the rifle shot ok to start with, I think I am going to set the barrel up on centers and re-cut the tapered O.D. to get the bore in the center of the barrel. The muzzle will still be larger after being cut than it was from the factory, and at this point I dont think I could screw it up much worse than it is.

The bore was in the center of the muzzle before being cut, so I guess my question is, "is this a common occurance with factory barrels?"
 
Off Center

To expand on what Mickey said, it is a LOT more common than most realize. Even in custom barrels, but not to the extent that you are experiencing with your Factory Savage.

That gives you a pretty good indication as to just how 'crooked" barrels are. By crooked, I mean how straight the ID is with its own self.

I see that you fell into that old wives tale of a barrel that is "stiffer" is more accurate. What you probably did is nothing more than cutting your overall velocity potential down. 20 inches is ngetting on the short side for a 223. I doubt you will see any measurable improvement in accuracy at all.

The quality of the bore, and other perameters of barrel quality, such as stress, are the defining factors in determining the accuracy potential of a barrel.........jackie
 
Barrel out of round

I have had several barrels from a top barrel maker be out as much as .040. when the bore and muzzle were dialed in and the .0001 indicator need was not moving at all. In the 50s and 60s I saw many military rifle barrels shortened and sportorized. Many when inspected their bores were out of center. The geometry of drill bits has greatly improved as has deep hole drilling.

Nat Lambeth
 
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sbindy said:
I am doing some work to my Savage in .223, and I shortened the barrel to 20". Partly to make the barrel stiffer and shoot better, and to get rid of a spot near the muzzle the fouled badly. After shortening, I noticed the bore wasnt in the center of the barrel anymore, and measured it. One side was .310, the other was .332!
Click to expand...

Two thoughts:

  1. When you recut the crown you might give some consideration to making sure you cut it perpendicular to the axis of the last half inch or so of the bore at the muzzle.
  2. Returning the OD of the barrel to put the bore at the muzzle in the center may cause issues with residual stresses that will end up making the barrel significantly less accurate.
Fitch
 
Rflshootr said:
.400??? holy cow!
Click to expand...


Well let's see...... with a .950 diameter barrel you'd subtract the bore diameter, let's say .243....

So even with my rudimentary math skills I see .707 left over. You divide this by 2 to get a POSSIBLE .353.5 per sidewall.....

dZEEPers, that puts the bore outside the barrel!!!

:D

Yup, methinks it's a typo...

LOL

al
 
alinwa said:
Well let's see...... with a .950 diameter barrel you'd subtract the bore diameter, let's say .243....

So even with my rudimentary math skills I see .707 left over. You divide this by 2 to get a POSSIBLE .353.5 per sidewall.....

dZEEPers, that puts the bore outside the barrel!!!

:D

Yup, methinks it's a typo...

LOL

al
Click to expand...
Picky-picky-picky ;)
 
Update

I recut the O.D. of the barrel, recrowned and installed the barrel. Its old favorite load of 42 1/4 clicks of Benchmark shot best with 1 click off the measure. This rifle shot much better with NS cases and I had to FL them since I reinstalled the barrel.

I will try it again with NS cases if the weather holds out. I also shot some 69gr SMK's with some new powders and AA2520 and BL-C(2) will get some more trials.
 
Rember that picture of the guy looking through a barrel mounted in this big thing called a barrel straigntening press. He's got a pile of newly made barrels and he is bending them each to get the bore straight. Standard manufacturing procedure. It was the last thing done. It was more likely that the bore was not concentric that that it was.
 
Sbindy,

I'm with you. I usually cut down an off center sporter barrel to make the bore concentric to the outside when there is the opportunity/thickness to do it. You can't always make it perfect, but you can make it better. For light barrels, the point is to make the thickness about the same all around the bore. If too far off center, the barrel will walk the shots in a line as the barrel heats - differential expansion makes the barrel bow. There may be some barrels that will "unkink" after straightening, and heavy turning of a barrel may also unleash some residual stresses, but i believe that the walking is usually due to the uneven barrel thickness, whatever it's cause. If you wish to see the effect in spades, shoot a drilling (three barrel gun, with high power rifle under double shotgun). At a hundred yards, the second shot will usually be 3-4 inches or so high from the first shot if shot quickly. This is because the very light rifle barrel heats rapidly, but is held against the shotgun barrels on one side, making the barrel bow. Slow groups will be very accurate in the same gun. This same effect happens to a lesser extent when not bound by the shotgun barrels, but it does happen. Food for thought, anyway.

Scott
 
shevelin said:
"If too far off center, the barrel will walk the shots in a line as the barrel heats - differential expansion makes the barrel bow."


Scott
Click to expand...


So Scott,

Before you shortened the barrel and re-turned to make it "concentric" was that area better? Why didn't it walk the shots before it was cut off?

al
 
One of the best .30 cal. BR barrels I've ever owned had the bore off by close to .035 at the muzzle. After some discussion, Stan installed it with the 'thick' side at 6:00.

If you don't 'clock' the thick/thin at 12:00/6:00, barrels like this can be particularly snotty for giving angular displacement as you go up and down with the powder. We've all seen the occasional odd BR rig that gives horizontal during tuning that isn't there on the flags.

Connecting those dots ain't hard............;)


"That's all I'm gonna' say 'bout that." -Forrest Gump.
 
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