I bought a concentricity gauge, then I checked some 6BR loaded rounds. WOW, some were out by .004 to .006 Total Indicator Reading.
So having read about the SAC bushings, I bought a couple, and put them in my full length sizing die instead of the Redding TiN bushing I generally use. (die by a big name company that I will not name, more on that later)
Result was........... NO better concentricity.
Next step, I purchased a Redding FL bushing die. Tried it with my original Redding TiN bushing.
Result was...... all concentricities were below .001 TIR
I stopped there, I did not check with the SAC bushings, because I felt that it was good enough. I also believe it was my original sizing die that was not concentric, not the bushings. I will try the SAC again some day. I also plan, some day, on the offending die, to indicate the bushing end diameter and compare it's concentricity to the neck and body diameter concentricities.
What if that die shows "perfect, or very, very low concenticity numbers? Then I would have to conclude it was operator error, and I screwed up somehow.
I have seen in this thread some negative comments on name brand dies/bushings, including the Redding which I found to be excellent. I believe it is the individual part that may be bad, not the product line, or there is operator error, which is the reason I declined to name the die I felt was not concentric.
Did I waste my money on the SAC bushings? NO, I will use them some day.
Did I waste my money on the original sizing die? NO, I still need to prove it faulty or not.
Nobody said this hobby was cheap.