Concentricity in reloading v chambering?

[Curious]

A lot is talked about concentricity while chambering and working to small tolerances like 0.0002" or less at key points.

I can understand a machinists desire to do this, I can also understand the concept of positioning the bullet as close to the centre line of the bore as possible to minimise the possibility of the bullet canting as it enters the rifling. I also get the idea of making sure all of the other critical faces are square, tenon shoulder and bolt face etc. So we work to achieve the tightest tolerances we can during the build.

Then we come to the ammunition?

I reload but I dont own a concentricity gauge so I have no idea how concentric my bullet is within the case neck, how concentric my dies make my cases or how my chamber will position my case to keep things as close to the tolerances I might try to build my rifle.

I appreciate that the best levels of overall accuracy will require the best levels of reloading accuracy as well as rifle chambering accuracy but how many of us come anywhere near achieving this? If I put a round into my 0.0002" chamber that is running out 0.002" then would it matter if the chamber was that good as surely the loaded round screws the previous good work up?

Please excuse the fact I have a habit of sometimes over-thinking things but the more I look into building an accurate rifle I more I realise I have far more questions than answers!

 

[jackie schmidt]

We strive to achieve the best results in the things that we have the most control over.

Since we can hold those tight tolerances much easier in chambering a barrel than we can assembling dozens of of rounds of ammunition at the same level of accuracy, that is what we do.

Is a bullet exiting a truly straight round and entering an out of alignment throat the same as as a bullet exiting a crooked round but entering a truly straight throat?

I don't know.

 

[DeltaBravo]

I've checked loaded round concentricity with the Sinclair and the 21st Century tools. My runout was not worth worrying about. I use a Redding bushes sizing die and a Wilson seating die. I think if you have a good barrel/chamber and pay attention during reloading and use good tools, you'll be okay. YMMV

Dennis

 

[JerrySharrett]

In benchrest chambers we have, generally. 0.002" or less clearance between the case neck and the chamber neck. Having precision turned the case necks to probably 0.00005" or less concentricity OD to Id. Having in most situations jammed the bullet into the throat cone the bullet will start out very well aligned.

In a SAAMI spec barrel where there is up to 0.010" clearance between the chamber neck and the case neck and the lawyers mandate bullet jump it is fairly certain there could be some in-bore yaw that doesn't help accuracy.

As to using a concentricity gage and trying to eliminate runout, I see this as a waste of time. If you have runout in your load seating, then try to push the bullet "straight" one thing that will happen is you will disturb the neck tension..


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