Tim L wrote:wsftr wrote:
IMO you can have brass that has an uneven neck and still be concentric to the bore, you can have even necks and a bullet that isn't concentric to the bore
Agreed, but
Can the projectile be concentric with unturned brass that is sized in a bushing die?
If the neck is uneven and it is sized from the outside, won't that put the inside off centre?
Or
Are we saying that neck clearnce means neck wall variation is irrelevent because it doesnt touch anything and the brass is actually centered from the case wall?
Or
Are both contentions irrelevant and concentricity is actually achieved buy having suitable clearence in both with freebore centralising the bullet?
mmm TBH we are talking different things.
Concentricity is one subject and clearance is another with neck thickness consistency another. There is a relationship between all 3 though.
IMO how even neck walls are relates to the way the neck releases the bullet...as does the overall thickness of the walls. As mentioned you can have very consistent neck thickness and still the neck is not concentric with the case. I bet most turn necks and measure necks with a ball micrometer. This does not measure concentricity.
There is a relationship between all 3 in that the case neck expands to seal against the chamber wall. The way it does this affects precision. A significantly uneven neck would touch the chamber at different timing/points and thus could affect precision. So even necks is best....but how uneven do they have to be before you can see a difference on paper? I would suggest that for many (buffalo boys) <.015" gets swallowed up in the noise. Noise being at least .5moa vertical at 1k.
From a precision point of view (ease of use is another topic) clearance relates to time. The time it takes for the neck to expand to seal. This time is also affected by the thickness of the neck. The thickness of the neck will also impact how much pressure is built before movement occurs by either the neck or bullet. I expect this time will affect harmonics and pressure and gas shape stuff like that. Anecdotally it appears that calibers such as .308 and 7mm prefer thicker necks and more time before seal takes place. I wouldn't be surprised if there was another combination of neck thickness and clearance that produced the same level of precision though...more - why would you bother KISS.
Concentricity is an interesting subject as there are various tools out there that measure it. Some methods are good at detecting all forms of concenticity others not so much. I don't have the articles at hand that discuss this suffice to say that using a common tool to measure bullet run out I can't see a difference on paper where run out is < .002".
For runout on my turned vs unturned brass I still ended up with run out of <.002" and no difference on paper. This simply told me the tolerance of modern good brass was within the tolerances of my other reloading practices such as bullet seating and not a significant contributor to be improved upon within my precision requirements on paper.
Yes theoretically an uneven neck sized from the outside pushes that uneveness to the inside (why do we outside neck size anyways
).
But then we get a big lump of lead and copper and force the neck to expand out again.....hmmm what is actually going on with respect to concentricity...
All in all even necks are best. Concentric loads are best. The question for most shooters is - at what measurement of tolerance do I notice a difference.