Is it possible for the bore and the chamber to be non-concentric ?

[340 in Va]

There's a fantastic episode of the Hornady podcasts with Jeff Siewert (spelling could be wrong) that talks about this and many other items. Barrel specific.
He is one of the worlds foremost barrel testers and examiners for the military.
With your point in particular, I remember there being cases where non concentric barrels being more accurate than some that are due to 'disturbed vibration' (think harmonics) and a bunch of other idiosyncrasies.
Anyway, better to watch the podcast rather than listen to me.
Really informative.

Thanks for the post, may take some time to digest. Can you believe 30-06 165 gr. was his bullet and cal. of choice? That should start a fire storm. I just finished load development on 06 with 165 interbonds for wife's Tikka yesterday.

 

[Radman]

Barrel manufacturers do not straighten barrels, it's true no barrel is perfectly straight from end to end. The Deep hole drilling machine is the major culprit on how straight a blank is from end to end.
This is why in my opinion a good smith who indicates at the throat is who I want chambering my barrels.

One of the first steps Savage barrels undergo is straightening - if needed. I'm sure there are others. (Check it out)

 

[RichCoyle]

Absolutely!

 

[Crockett12]

I had a .338 Win Mag in the early Ruger 77 with the boat paddle stock that had an off center bore. I never measured how off center it was but it was obvious to the naked eye when you looked closely! Didn't realize it until I had issues with accuracy once the barrel got hot at the range doing load testing. Sold it to a hunter who didn't care and bought another of the same model and it was bored correctly and very accurate!

 

[Taj]

One of the first steps Savage barrels undergo is straightening - if needed. I'm sure there are others. (Check it out)

You are correct, Savage as do many others do straighten barrels. That creates another issue if they are not stressed relieved after straightening. When a barrel is straightened it creates stress (Compression and elongation) where the straightening bends are made. If the barrel is not stress relieved after the straightening process, the barrel will try to move back to it's original condition when it gets hot. Barrels can be cryo or heat stress relieved. If heated it is usually done in an inert atmosphere. Improper or zero stress relieveing of a straightened barrel can cause wandering groups.

 

[Rocketeer77]

I would think that if the barrel is centered in a lathe when the chamber is cut and reamed,
then the chamber would always have to be concentric with the bore, because that is how
the rifle bore itself is cut. Same with the barrel threads.
The outside surface contour of the barrel also must be concentric for the same reason,
although this is of somewhat less concern.

I'm trying to eliminate things to worry about. If the brass or ammo is out-of-round, that can be
dealt with separately and solved. I'd really like to believe that the barrel is never part of some
out-of-round problem.

As a machinist in a past life you are assuming far too much, there's a myriad of screw ups possible.

Machinist doesn't care
Incompetence
Poor equipment
Mistakes
No QA procedures
Stupidly
Etc

 

[Bowfisher]

I would submit that the PERFECTLY concentric bore/chamber job , is the anomaly and not the rule. Most of them are off to some degree.

 

[Wyowind]

I have seen a number of Remington rifles where the chamber and the barrel were clearly not aligned. With a bore scope it was possible to see where the lands started on the receiver end of the barrel. Looking over 360 degrees, you could see lands on one side but none on the other until some little distance down the barrel.

Surprisingly this did not necessarily have adverse effects on accuracy, at least on a hunting rifle. It might be a different story on a target rifle where expectations would be higher.

One rifle was far enough off that Remington factory ammunition was giving high pressure signs. The bullet was having to straighten out after entering the barrel in a crooked fashion that was not in line with the center of the bore.

I do not know how Remington made their barrels and chambered them. But clearly it was possible for the barrel and the chamber to be mis-aligned.

Remington, and others, did not regard this as a fault unless the accuracy was outside their specs.

WyoWind

 

[L.Sherm]

One of the first steps Savage barrels undergo is straightening - if needed. I'm sure there are others. (Check it out)

All the more reason for me not buying a savage. I was talking custom barrel manufacturers i guess I should have specified.
I know somebody is gonna roast me about my savage comment but when you have made barrels you will know why I said that. When you complete a barrel and you manipulate the steel afterwards trying to straighten it what do you think happens, its gotta stretch and induce stress.
I've talked with some good BR smiths who have told me they have got some pretty crooked bores( crescent) ones to shoot really well he just thought the " nodes" with the straighter ones were larger.
I really doudt that after the " straighting" process they stress relieve them again.
What really are they trying to straighten?
Are they putting them in a lathe and dialing them in to see how far there off or just inserting pins in the ends and rotating them.
If there that crooked they need straightening they should never be put on a rifle anyway.

 

[L.Sherm]

This was posted by J.E. a few years back and he hit the nail squarely on the head

 

[QuietTexan]

This seems pretty fundamental, how can it go wrong ?

You're making the assumption that the hole is straight to start with. A lot of barrels won't take a pin gauge down the length of the bore because of deflection while drilling. Hence the never ending debate over dialing the ends of the bore, or dialing ahead of the reamer.

I've had barrels dialed end to end shoot better than ones dialed in off the throat end. There's more variables at play than can be reduced on any given blank.

 

[L.Sherm]

A drill is only the start of the bore, the bore reamer is what makes it the final dimension but just like any reamer it will only follow what essentially is the pilot hole made by the drilling process

 

[randy86314]

I have used primarily Douglas barrels. "Premium" barrels are not straightened. If it isn't Premium, it was straightened. Air gauging is a different topic.
It's not real difficult to center a barrel for threading and chambering, but it's easy to screw it up without basic setup technique. (I use reamers with interchangeable pilots and a floating reamer holder.) I don't indicate off a pin inserted in the bore.
btw, Most of my reamers are PT&G, and they all are excellent?

 

[Radman]

As a machinist in a past life you are assuming far too much, there's a myriad of screw ups possible.

Machinist doesn't care
Incompetence
Poor equipment
Mistakes
No QA procedures
Stupidly
Etc

I would think that if the barrel is centered in a lathe when the chamber is cut and reamed,
then the chamber would always have to be concentric with the bore, because that is how
the rifle bore itself is cut. Same with the barrel threads.
The outside surface contour of the barrel also must be concentric for the same reason,
although this is of somewhat less concern.

I'm trying to eliminate things to worry about. If the brass or ammo is out-of-round, that can be
dealt with separately and solved. I'd really like to believe that the barrel is never part of some
out-of-round problem.

One thing I see us straying away from (me included) as this post evolves is chamber vs barrel concentricity.

All the more reason for me not buying a savage. I was talking custom barrel manufacturers i guess I should have specified.
I know somebody is gonna roast me about my savage comment but when you have made barrels you will know why I said that. When you complete a barrel and you manipulate the steel afterwards trying to straighten it what do you think happens, its gotta stretch and induce stress.
I've talked with some good BR smiths who have told me they have got some pretty crooked bores( crescent) ones to shoot really well he just thought the " nodes" with the straighter ones were larger.
I really doudt that after the " straighting" process they stress relieve them again.
What really are they trying to straighten?
Are they putting them in a lathe and dialing them in to see how far there off or just inserting pins in the ends and rotating them.
If there that crooked they need straightening they should never be put on a rifle anyway.

Most often they're straightening what shippers & materials-handling people have bent (cold) by either wrapping one sling around the center of a bundle of bar stock and the ends bend down or the load is slung near the two ends & the center swags down. I've seen it in industries for years. Either way the steel gets bent COLD & some manufacturers straighten it COLD so there is no heat involved so far. That comes later down the line.
Either way, it wasn't stipulated, just stating that barrel makers don't straighten barrels.
Try drilling a hole through a warped broom handle. Even if clamped perfectly square in a lathe, after it's released you'll still have a bowed broom handle (or gun barrel). Straightening before machining is the only way to assure a truer barrel. (I can't imagine trying to to cut bollard rifling in an untrued barrel)
We haven't even discussed cold hammer-forged barrels, (which are also great), & gotten way off original topic of barrel/chamber concentricity, which is what this was originally about.
I am not here to attack a particular brand or to force my opinion. I just know that (good) barrel makers DO straighten barrels if needed. To do that for mass production is incredible.