Redding Competition shell holders: Depends, my opinion they come under the category of nice to have but not necessary, then there is the “You ‘gotta" have...etc..
I have one set, a #6 set for magnum cases like 300 Win Mag etc.. there is 5 shell holders in a set, each one is suppose to increase the length of the case from the head of the case to the shoulder .002”, not a problem, 3 of the five in my set are off .001”, Without the Redding Competition shell holder I have 10 options between .000 and .010, that is 5 more options than I had when I did not have the Redding set. When I am discussing the need for ‘a tool’ I never know if I am discussing the tool with the person that manufactures and sells the tool or someone that want a fair and or objective opinion. Again, my dies and presses have threads, the threads make my dies adjustable in the press, that leaves the ‘how to adjust’ part. I use the feeler gage to adjust the gap between the top of the shell holder and bottom of the die, then comes the difficult part, knowing how much gap when adjusting the gap, I determine the length of the chamber first.
The Redding os on the + side, with the feeler gage I can make adjustment on the – side, for short chambers? Forming cases for short chambers that are .012” shorter than a minimum length case does not create a problem when using a RCBS shell holder, with the Lee shell holder add about .003”.