Shoebox
So glad you asked. I have some thoughts on concentricity. Now with our Twisted Barrel tech coming into its own, the next big huddle to overcome in the pursuit of accuracy is the concentricity of the handloaded metallic cartridge. We all know that concentricity has nothing to do with the brass itself. after all, it is manufactured with such care and such close tolerances that can easily be measured with a concentricity gauge and a hacksaw, or a mic and a loop. It is well known that firing a case in a chamber (especially one that has been twisted) will result in a perfectly formed case, due to that fraction of a moment when it turns to an elastic molten polymer and then snaps back to a solid. Then we take that perfect brass and run it cold thru a die. And lo and behold it shows up a lack of concentricity. Now we can fiddle with the brass, cutting the dreaded carbon donut out, or pressing the thing to the outside and burnishing the neck with a case neck turner, but that does not change the die. and it is the die that is the problem. Simply look at all the threads about neck sizing, full length sizing, bushing sizing, headspace and what all. What does it all have in common? It is plain as the ear on your head that it is the dies.
As I mentioned in an earlier answer, I have developed a honing method for my bushing dies. It involves a chicken bone (properly seasoned) and JB paste. Two commonly available components in any shooters bag. It is the PROCESS that together with the proper tools that created concentric brass, the pancreas of all accuracy endeavors.
Man this is good stuff, I will add it to my techniques manual, so just a question or two, I'm so excited I don't no what to ask first, OK important stuff first !!
What breed of chicken - age of bird - left or right leg, I notice you said properly season , I don't want to infringe
But could you tell me seasoning type/types, weight's and application procedure, also straight drive or rotational reaming, be assured this info will be for my eyes only!
This will tighten that 900 yrd group !!!
I'm not sure if a man with your highly technical approach, would consider a layman method, but here goes, as you stated the die is the weak point, so i rarely use them, most people fire form brass, they are missing the point
"fire form the chamber"
Yes I know it's so obvious !! Quick run through of process
First measure OD of chamber ,
Acquirer a bullet one caliber larger than bore heavier the better ie 257 - 264 this allows required gas seal !
Prime with hottest mag primer you can get! Fill case with blue dot or similar fast powder
In my case 93 grn then compress hammer and 1/4" drill for my particular applications be careful not to damage neck, compress - fill - compress- fill I get 115.6 grain in with slight case bulge
Recompress when seating bullet
Load bullet in chamber if all is going well you will need rubber mallet will only take 6-10 good stiff strikes to close, hey ready to go !!
Go out the back and squeeze of a shot
Believe me this will straighten out everything, (oh ear protection safety first )
Now unload may need mallet again?
Check for primer, if any sign of primer is found start process a gain !!!
Measure OD of chamber 2-3 mm expansion is standard, 3 -4.5 mm is much desired
If you are really pedantic you could recontour chamber but the barrel may take a bit of getting out
So now you have a chamber that is dead straight no need for dies, fireform and a light crimp
Concentricity what so hard about that !!
Your results may vary ?