Re: Concentricity:How much ?
Iíll have to say, as much as I really enjoy reloading, I have been trying to avoid neck turning as long as possible. As I mentioned earlier, I have sorted my brass by neck wall variation and I believe it has worked well for me up to this point. I have always tried to maintain two piles, one that was .001 or less and the other that was .001 to .002. To be honest, I donít know if these two piles shot any different or not. Also, TIR pretty well matched the variation measurements.
JE, as you know, lately Iíve been having some major runout issues with Rem 300 Ultra brass. I did a test a while back with 9 rounds, measuring the brass during every step of the process. I sorted new cases by neck wall variation. I couldnít be too picky with this but ended up with the best three having neck wall variations of .0015, .0015, and .0025. The runout at the neck was .0015, .002, and .0025. Neck wall variation pretty much stayed constant with runout. Loaded round TIR as measured at the ogive was .0015, .002, and .0025. Again, fairly constant at this point. At the bench, these three rounds shot a center to center of 0.25 at 100 yds.
Now, some of the other cases started out with neck wall variations of .0035, .0035, and .003. TIR at the neck was the same. TIR at the ogive was .007, .006, and .006. It was almost like a trickle effect. They started bad and just got worse, doubling when measured at the ogive. I guess this may be due to the measurement being taken farther down the case in that it becomes more apparent. These shot fairly well with a measured group of 0.4. I was a little surprised they did as well as they did, but the group size did increase, almost doubled.
Finally, the worst cases of the bunch were neck variation of .0045, .0045, and .005. TIR at the neck was .0045, .0045, and .005. Again, the same. TIR at the ogive was .0065, .0075, and .009. These three shots were loaded the same, just had terrible runout numbers and the group opened up to 1Ē+.
Unfortunately I am unable to find decent brass in this caliber, atleast for the time being. I have a feeling that neck trimming would be beneficial to the overall accuracy potential of this brass.
TnTom, ď If the necks are pliable, clean and the walls are relatively uniformĒ. That sounds like solid advice. I have noticed in other calibers when the brass starts to get a little hard around the necks. I havenít tried annealing yet but have been reading up on it as well.
During this test, I weighed all of the brass and could not find any correlation between this. Also, naturally this is not a scientific test under a controlled environment, just one guy messing around at the bench. Hope it helps.