Changing the lock ring that use the lock screw against the threads to the older type that squeezes the lock-ring against the threads (Hornady Type) will also be one extra simple step to take.
Also, I will take 2 shell holders and place them onto the PRESS RAM so that I can get a completely flat surface to mate against the seating die to make sure that the die is inline with the shell holder (The single shell holder in the ram usually will not make contact with the bottom of the seating die, so it may not be inline). Then I will tighten the lock-ring down.
Just a couple of other things you may want to try that do not cost anything other than time.
As far as the question of which concentricity gauge I use? I use the RCBS gauge, but would prefer one that uses the steel balls rather than flat aluminum bars to place the cases on to measure.
Now I do not shoot competition, but just like to know that I have done the most I can do to get a factory rifle and my reloaded ammunition to do the best it can and to be able to place a bullet where it needs to go as long as I do my part. Do I use match or custom brass like Lapua? NO, I use what brass that is commonly available to all us reloaders and use it to make the best ammunition that I can out of it. I have groups usually in the range of 3/8 inch in spread and have had loads go "BUG HOLE" also. These days, the gun is probably better than me, as I do not get so shoot everyday like I used to.
JOHN
