Off-center bore -

[ppb]

I'm at a point in a current build when it's time to solder the under rib and and RR pipes to the barrel. But I wanted to re-crown the muzzle before the the rib and pipes went on.

Got the lathe set up with the four jaw chuck made sure it was true, put in the barrel spider, trued it up, and powered up the lathe to make sure the set-up was good.

When I looked at the muzzle, the bore was loping around as though there was some sort of internal cam orifice in there. Rechecked my set-up, then I got out the indicators and found the factory chamfer to the flats had a .004" run-out. I would think that to be acceptable. ( 7/8" bbl) The chamfer to the bore looked good. But now, I suspect that chamfer was not done on a lathe, but with a tool that uses a guide rod inserted into he bore... Regardless, the bore indicated a .025" swing in one revolution. I thought that to be weird and highly suspect. I am also thinking it is not acceptable from today's barrel makers. ( I made some videos w/my phone but am not able to get them posted.)

The barrel was made by a reputable barrel maker and came from a reputable supplier.
Is this a fluke or is this sort of thing going to be standard fare in the future?

 

[hawkeye2]

Who made the barrel? Douglas? They were known for runout and stamped the barrel on what was to be the bottom flat to orient it vertically. Fit the barrel up so that the runout is in the vertical plane (up). I believe you are right about the chamfer being done by a tool with a guide in the bore. If the barrel was drilled from 7/8" octagonal stock where will be some runout. That runout does sound excessive and I believe it's a fluke.

 

[ppb]

Thanks for your input, Hawkeye2!
I appreciate the value of your experience.

The problem is that this barrel (Colerain) has already been fitted - because, like a dummy, I trusted the brand and it came with the breech plug/tang installed.
The only remaining tasks before finishing the rifle out are sight dove tails, the rib/pipes and barrel prep.
Not that it can't be done, but working through a "do-over" will be a pizzer of the highest order.

 

[user 34300]

I have run into several that shoot about 6" left @ 50 yards, with the sights centered.. Since the outside is straight that means the bore is crooked. Moving the sights a total of over 0.100" total offset looks weird and messes with the cheek weld. My solution is to bend the barrel. That is not a perfect solution. Because there is more material on one side of the bore as the barrel heats is bends more. It is a problem for load testing because the point of impact walks. So, it seems common. I doubt they are checking the bores for straightness. I speculate that people with those skills are not working in production barrel making operations anymore.

 

[Eric Krewson]

I got one like that, Colerain bent over backwards to make me happy, they replaced the barrel and said I could have any of their barrels for free or keep the off center barrel to compensate me, I had already had the barrel jug choked and fitted to my gun before I noticed the off center bore. I kept the already jug choked barrel and gave it to a friend who made a great turkey gun with it.

 

[bptactical]

This is why you inspect your components very carefully before investing time in fitting.

Put the runout at either 12:00 or 6:00.
It’s easier to compensate for it in the elevation plane instead of chasing windage issues.

 

[Nor Cal Mikie]

First thing I would look at is? How does it shoot???

I kept the already jug choked barrel and gave it to a friend who made a great turkey gun with it.

Then there's that.
Never notice it being off center @ 20MPH on a fast horse.

 

[user 34300]

This is why you inspect your components very carefully before investing time in fitting.

Put the runout at either 12:00 or 6:00.
It’s easier to compensate for it in the elevation plane instead of chasing windage issues.

If the barrel has the breech plug, and dovetails already installed you are stuck......

 

[ppb]

Scota@4570,

There's a high probability that you are correct in thinking I'm stuck.

In theory however, it may be possible to rotate the breech plug (which would involve some tedious machine work) the seven flats needed to orient the runout to the vertical plane. Fortunately, I haven't drilled the flash hole yet, but then the barrel lug would need to be rotated to the next flat, also.. The math says 7/8 of a revolution of the plug would only shorten the barrel by @ .049" Of course that's theory. The practical side of it remains to be seen...

I've had the breech plug off once before - for barrel fitting- and it appears as though the threads in both the barrel and breech plug had been pulled to get a "tight fit." So that may be a problem in-and-of itself.

Thanks for your interest!